diff --git a/BUILD b/BUILD
index 202154c9d0..bcecd387af 100644
--- a/BUILD
+++ b/BUILD
@@ -28,6 +28,8 @@ exports_files([
 
 CPPOPTS = [
     # copybara:strip_for_google3_begin
+    "-Wextra",
+    # "-Wshorten-64-to-32",  # not in GCC (and my Kokoro images doesn't have Clang)
     "-Werror",
     "-Wno-long-long",
     # copybara:strip_end
@@ -164,6 +166,10 @@ cc_library(
     hdrs = [
         "upb/text_encode.h",
     ],
+    copts = select({
+        ":windows": [],
+        "//conditions:default": COPTS,
+    }),
     visibility = ["//visibility:public"],
     deps = [
         ":port",
@@ -181,6 +187,10 @@ cc_library(
         "upb/json_decode.h",
         "upb/json_encode.h",
     ],
+    copts = select({
+        ":windows": [],
+        "//conditions:default": COPTS,
+    }),
     deps = [
         ":port",
         ":reflection",
diff --git a/generated_for_cmake/upb/json/parser.c b/generated_for_cmake/upb/json/parser.c
index 34571880f4..dd4fd82f2f 100644
--- a/generated_for_cmake/upb/json/parser.c
+++ b/generated_for_cmake/upb/json/parser.c
@@ -977,6 +977,7 @@ static bool parse_number_from_buffer(upb_json_parser *p, const char *buf,
         upb_sink_putint32(p->top->sink, parser_getsel(p), (int32_t)val);
         return true;
       }
+      UPB_UNREACHABLE();
     }
     case UPB_TYPE_UINT32: {
       unsigned long val = strtoul(buf, &end, 0);
@@ -988,6 +989,7 @@ static bool parse_number_from_buffer(upb_json_parser *p, const char *buf,
         upb_sink_putuint32(p->top->sink, parser_getsel(p), (uint32_t)val);
         return true;
       }
+      UPB_UNREACHABLE();
     }
     /* XXX: We can't handle [u]int64 properly on 32-bit machines because
      * strto[u]ll isn't in C89. */
@@ -999,6 +1001,7 @@ static bool parse_number_from_buffer(upb_json_parser *p, const char *buf,
         upb_sink_putint64(p->top->sink, parser_getsel(p), val);
         return true;
       }
+      UPB_UNREACHABLE();
     }
     case UPB_TYPE_UINT64: {
       unsigned long val = strtoul(p->accumulated, &end, 0);
@@ -1010,6 +1013,7 @@ static bool parse_number_from_buffer(upb_json_parser *p, const char *buf,
         upb_sink_putuint64(p->top->sink, parser_getsel(p), val);
         return true;
       }
+      UPB_UNREACHABLE();
     }
     default:
       break;
@@ -2575,11 +2579,11 @@ static bool does_fieldmask_end(upb_json_parser *p) {
  * final state once, when the closing '"' is seen. */
 
 
-#line 2780 "upb/json/parser.rl"
+#line 2784 "upb/json/parser.rl"
 
 
 
-#line 2583 "upb/json/parser.c"
+#line 2587 "upb/json/parser.c"
 static const char _json_actions[] = {
 	0, 1, 0, 1, 1, 1, 3, 1, 
 	4, 1, 6, 1, 7, 1, 8, 1, 
@@ -2834,7 +2838,7 @@ static const int json_en_value_machine = 78;
 static const int json_en_main = 1;
 
 
-#line 2783 "upb/json/parser.rl"
+#line 2787 "upb/json/parser.rl"
 
 size_t parse(void *closure, const void *hd, const char *buf, size_t size,
              const upb_bufhandle *handle) {
@@ -2857,7 +2861,7 @@ size_t parse(void *closure, const void *hd, const char *buf, size_t size,
   capture_resume(parser, buf);
 
   
-#line 2861 "upb/json/parser.c"
+#line 2865 "upb/json/parser.c"
 	{
 	int _klen;
 	unsigned int _trans;
@@ -2932,147 +2936,147 @@ _match:
 		switch ( *_acts++ )
 		{
 	case 1:
-#line 2588 "upb/json/parser.rl"
+#line 2592 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 2:
-#line 2590 "upb/json/parser.rl"
+#line 2594 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 23;goto _again;} }
 	break;
 	case 3:
-#line 2594 "upb/json/parser.rl"
+#line 2598 "upb/json/parser.rl"
 	{ start_text(parser, p); }
 	break;
 	case 4:
-#line 2595 "upb/json/parser.rl"
+#line 2599 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_text(parser, p)); }
 	break;
 	case 5:
-#line 2601 "upb/json/parser.rl"
+#line 2605 "upb/json/parser.rl"
 	{ start_hex(parser); }
 	break;
 	case 6:
-#line 2602 "upb/json/parser.rl"
+#line 2606 "upb/json/parser.rl"
 	{ hexdigit(parser, p); }
 	break;
 	case 7:
-#line 2603 "upb/json/parser.rl"
+#line 2607 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hex(parser)); }
 	break;
 	case 8:
-#line 2609 "upb/json/parser.rl"
+#line 2613 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(escape(parser, p)); }
 	break;
 	case 9:
-#line 2615 "upb/json/parser.rl"
+#line 2619 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 10:
-#line 2620 "upb/json/parser.rl"
+#line 2624 "upb/json/parser.rl"
 	{ start_year(parser, p); }
 	break;
 	case 11:
-#line 2621 "upb/json/parser.rl"
+#line 2625 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_year(parser, p)); }
 	break;
 	case 12:
-#line 2625 "upb/json/parser.rl"
+#line 2629 "upb/json/parser.rl"
 	{ start_month(parser, p); }
 	break;
 	case 13:
-#line 2626 "upb/json/parser.rl"
+#line 2630 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_month(parser, p)); }
 	break;
 	case 14:
-#line 2630 "upb/json/parser.rl"
+#line 2634 "upb/json/parser.rl"
 	{ start_day(parser, p); }
 	break;
 	case 15:
-#line 2631 "upb/json/parser.rl"
+#line 2635 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_day(parser, p)); }
 	break;
 	case 16:
-#line 2635 "upb/json/parser.rl"
+#line 2639 "upb/json/parser.rl"
 	{ start_hour(parser, p); }
 	break;
 	case 17:
-#line 2636 "upb/json/parser.rl"
+#line 2640 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hour(parser, p)); }
 	break;
 	case 18:
-#line 2640 "upb/json/parser.rl"
+#line 2644 "upb/json/parser.rl"
 	{ start_minute(parser, p); }
 	break;
 	case 19:
-#line 2641 "upb/json/parser.rl"
+#line 2645 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_minute(parser, p)); }
 	break;
 	case 20:
-#line 2645 "upb/json/parser.rl"
+#line 2649 "upb/json/parser.rl"
 	{ start_second(parser, p); }
 	break;
 	case 21:
-#line 2646 "upb/json/parser.rl"
+#line 2650 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_second(parser, p)); }
 	break;
 	case 22:
-#line 2651 "upb/json/parser.rl"
+#line 2655 "upb/json/parser.rl"
 	{ start_duration_base(parser, p); }
 	break;
 	case 23:
-#line 2652 "upb/json/parser.rl"
+#line 2656 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_duration_base(parser, p)); }
 	break;
 	case 24:
-#line 2654 "upb/json/parser.rl"
+#line 2658 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 25:
-#line 2659 "upb/json/parser.rl"
+#line 2663 "upb/json/parser.rl"
 	{ start_timestamp_base(parser); }
 	break;
 	case 26:
-#line 2661 "upb/json/parser.rl"
+#line 2665 "upb/json/parser.rl"
 	{ start_timestamp_fraction(parser, p); }
 	break;
 	case 27:
-#line 2662 "upb/json/parser.rl"
+#line 2666 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_fraction(parser, p)); }
 	break;
 	case 28:
-#line 2664 "upb/json/parser.rl"
+#line 2668 "upb/json/parser.rl"
 	{ start_timestamp_zone(parser, p); }
 	break;
 	case 29:
-#line 2665 "upb/json/parser.rl"
+#line 2669 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_zone(parser, p)); }
 	break;
 	case 30:
-#line 2667 "upb/json/parser.rl"
+#line 2671 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 31:
-#line 2672 "upb/json/parser.rl"
+#line 2676 "upb/json/parser.rl"
 	{ start_fieldmask_path_text(parser, p); }
 	break;
 	case 32:
-#line 2673 "upb/json/parser.rl"
+#line 2677 "upb/json/parser.rl"
 	{ end_fieldmask_path_text(parser, p); }
 	break;
 	case 33:
-#line 2678 "upb/json/parser.rl"
+#line 2682 "upb/json/parser.rl"
 	{ start_fieldmask_path(parser); }
 	break;
 	case 34:
-#line 2679 "upb/json/parser.rl"
+#line 2683 "upb/json/parser.rl"
 	{ end_fieldmask_path(parser); }
 	break;
 	case 35:
-#line 2685 "upb/json/parser.rl"
+#line 2689 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 36:
-#line 2690 "upb/json/parser.rl"
+#line 2694 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_TIMESTAMP)) {
           {stack[top++] = cs; cs = 47;goto _again;}
@@ -3086,11 +3090,11 @@ _match:
       }
 	break;
 	case 37:
-#line 2703 "upb/json/parser.rl"
+#line 2707 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 78;goto _again;} }
 	break;
 	case 38:
-#line 2708 "upb/json/parser.rl"
+#line 2712 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           start_any_member(parser, p);
@@ -3100,11 +3104,11 @@ _match:
       }
 	break;
 	case 39:
-#line 2715 "upb/json/parser.rl"
+#line 2719 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_membername(parser)); }
 	break;
 	case 40:
-#line 2718 "upb/json/parser.rl"
+#line 2722 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           end_any_member(parser, p);
@@ -3114,7 +3118,7 @@ _match:
       }
 	break;
 	case 41:
-#line 2729 "upb/json/parser.rl"
+#line 2733 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           start_any_object(parser, p);
@@ -3124,7 +3128,7 @@ _match:
       }
 	break;
 	case 42:
-#line 2738 "upb/json/parser.rl"
+#line 2742 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           CHECK_RETURN_TOP(end_any_object(parser, p));
@@ -3134,54 +3138,54 @@ _match:
       }
 	break;
 	case 43:
-#line 2750 "upb/json/parser.rl"
+#line 2754 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_array(parser)); }
 	break;
 	case 44:
-#line 2754 "upb/json/parser.rl"
+#line 2758 "upb/json/parser.rl"
 	{ end_array(parser); }
 	break;
 	case 45:
-#line 2759 "upb/json/parser.rl"
+#line 2763 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_number(parser, p)); }
 	break;
 	case 46:
-#line 2760 "upb/json/parser.rl"
+#line 2764 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 47:
-#line 2762 "upb/json/parser.rl"
+#line 2766 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_stringval(parser)); }
 	break;
 	case 48:
-#line 2763 "upb/json/parser.rl"
+#line 2767 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_stringval(parser)); }
 	break;
 	case 49:
-#line 2765 "upb/json/parser.rl"
+#line 2769 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 50:
-#line 2767 "upb/json/parser.rl"
+#line 2771 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 51:
-#line 2769 "upb/json/parser.rl"
+#line 2773 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 52:
-#line 2771 "upb/json/parser.rl"
+#line 2775 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_subobject_full(parser)); }
 	break;
 	case 53:
-#line 2772 "upb/json/parser.rl"
+#line 2776 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
 	case 54:
-#line 2777 "upb/json/parser.rl"
+#line 2781 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
-#line 3185 "upb/json/parser.c"
+#line 3189 "upb/json/parser.c"
 		}
 	}
 
@@ -3198,32 +3202,32 @@ _again:
 	while ( __nacts-- > 0 ) {
 		switch ( *__acts++ ) {
 	case 0:
-#line 2586 "upb/json/parser.rl"
+#line 2590 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; 	if ( p == pe )
 		goto _test_eof;
 goto _again;} }
 	break;
 	case 46:
-#line 2760 "upb/json/parser.rl"
+#line 2764 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 49:
-#line 2765 "upb/json/parser.rl"
+#line 2769 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 50:
-#line 2767 "upb/json/parser.rl"
+#line 2771 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 51:
-#line 2769 "upb/json/parser.rl"
+#line 2773 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 53:
-#line 2772 "upb/json/parser.rl"
+#line 2776 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
-#line 3227 "upb/json/parser.c"
+#line 3231 "upb/json/parser.c"
 		}
 	}
 	}
@@ -3231,7 +3235,7 @@ goto _again;} }
 	_out: {}
 	}
 
-#line 2805 "upb/json/parser.rl"
+#line 2809 "upb/json/parser.rl"
 
   if (p != pe) {
     upb_status_seterrf(parser->status, "Parse error at '%.*s'\n", pe - p, p);
@@ -3274,13 +3278,13 @@ static void json_parser_reset(upb_json_parser *p) {
 
   /* Emit Ragel initialization of the parser. */
   
-#line 3278 "upb/json/parser.c"
+#line 3282 "upb/json/parser.c"
 	{
 	cs = json_start;
 	top = 0;
 	}
 
-#line 2847 "upb/json/parser.rl"
+#line 2851 "upb/json/parser.rl"
   p->current_state = cs;
   p->parser_top = top;
   accumulate_clear(p);
diff --git a/kokoro/ubuntu/build.sh b/kokoro/ubuntu/build.sh
index 97678ea286..3888d15f6a 100644
--- a/kokoro/ubuntu/build.sh
+++ b/kokoro/ubuntu/build.sh
@@ -1,12 +1,18 @@
 #!/bin/bash
 
+set -ex
+
 # Install the latest version of Bazel.
-use_bazel.sh latest
+if [ -x "$(command -v use_bazel.sh)" ]; then
+  use_bazel.sh latest
+fi
 
 # Verify/query CMake
 echo PATH=$PATH
 ls -l `which cmake`
 cmake --version
+echo CC=${CC:-cc}
+${CC:-cc} --version
 
 # Log the bazel path and version.
 which bazel
diff --git a/tests/conformance_upb.c b/tests/conformance_upb.c
index 4a04adf8e4..fe9f5224e5 100644
--- a/tests/conformance_upb.c
+++ b/tests/conformance_upb.c
@@ -138,7 +138,7 @@ void serialize_json(const upb_msg *msg, const upb_msgdef *m, const ctx *c) {
   upb_status_clear(&status);
   len = upb_json_encode(msg, m, c->symtab, opts, NULL, 0, &status);
 
-  if (len == -1) {
+  if (len == (size_t)-1) {
     const char *inerr = upb_status_errmsg(&status);
     size_t len = strlen(inerr);
     char *err = upb_arena_malloc(c->arena, len + 1);
diff --git a/tests/json/test_json.cc b/tests/json/test_json.cc
index e5f0103584..18ab07fe50 100644
--- a/tests/json/test_json.cc
+++ b/tests/json/test_json.cc
@@ -149,6 +149,7 @@ static TestCase kTestSkipUnknown[] = {
 static TestCase kTestFailure[] = {
   {
     TEST("{\"optionalEnum\":\"UNKNOWN_ENUM_VALUE\"}"),
+    EXPECT("{}"),  /* Actually we expect error, this is checked later. */
   },
   TEST_SENTINEL
 };
@@ -242,7 +243,7 @@ void test_json_roundtrip() {
 
     for (size_t i = 0; i < strlen(test_case->input); i++) {
       test_json_roundtrip_message(test_case->input, expected,
-                                  serialize_handlers, parser_method, i,
+                                  serialize_handlers, parser_method, (int)i,
                                   false);
     }
   }
@@ -257,7 +258,7 @@ void test_json_roundtrip() {
 
     for (size_t i = 0; i < strlen(test_case->input); i++) {
       test_json_roundtrip_message(test_case->input, expected,
-                                  serialize_handlers, parser_method, i,
+                                  serialize_handlers, parser_method, (int)i,
                                   true);
     }
   }
@@ -274,7 +275,7 @@ void test_json_roundtrip() {
 
     for (size_t i = 0; i < strlen(test_case->input); i++) {
       test_json_roundtrip_message(test_case->input, expected,
-                                  serialize_handlers, parser_method, i,
+                                  serialize_handlers, parser_method, (int)i,
                                   false);
     }
   }
@@ -319,7 +320,7 @@ void test_json_failure() {
        test_case->input != NULL; test_case++) {
     for (size_t i = 0; i < strlen(test_case->input); i++) {
       test_json_parse_failure(test_case->input, serialize_handlers,
-                              parser_method, i);
+                              parser_method, (int)i);
     }
   }
 }
diff --git a/tests/pb/test_decoder.cc b/tests/pb/test_decoder.cc
index ef40f8f3e2..14fd72abbc 100644
--- a/tests/pb/test_decoder.cc
+++ b/tests/pb/test_decoder.cc
@@ -509,8 +509,8 @@ void do_run_decoder(VerboseParserEnvironment* env, upb::pb::DecoderPtr decoder,
     }
 
     bool ok = env->Start() &&
-              parse(env, decoder, i) &&
-              parse(env, decoder, j - i) &&
+              parse(env, decoder, (int)i) &&
+              parse(env, decoder, (int)(j - i)) &&
               parse(env, decoder, -1) &&
               env->End();
 
@@ -1108,7 +1108,7 @@ void test_valid() {
   run_decoder(buf, &textbuf);
 }
 
-void empty_callback(const void *closure, upb::Handlers* h_ptr) {}
+void empty_callback(const void* /* closure */, upb::Handlers* /* h_ptr */) {}
 
 void test_emptyhandlers(upb::SymbolTable* symtab) {
   // Create an empty handlers to make sure that the decoder can handle empty
@@ -1176,7 +1176,7 @@ extern "C" {
 
 int run_tests(int argc, char *argv[]) {
   if (argc > 1)
-    filter_hash = strtol(argv[1], NULL, 16);
+    filter_hash = (uint32_t)strtol(argv[1], NULL, 16);
   for (int i = 0; i < MAX_NESTING; i++) {
     closures[i] = i;
   }
diff --git a/tests/test_cpp.cc b/tests/test_cpp.cc
index 55cc077c88..4ca81e1c35 100644
--- a/tests/test_cpp.cc
+++ b/tests/test_cpp.cc
@@ -681,6 +681,7 @@ void DoNothingEndMessageHandler(C* closure, upb_status *status) {
 
 void RegisterMismatchedTypes(const void* closure, upb::Handlers* h_ptr) {
   upb::HandlersPtr h(h_ptr);
+  UPB_UNUSED(closure);
 
   upb::MessageDefPtr md(h.message_def());
   ASSERT(md);
@@ -797,6 +798,7 @@ void RegisterMismatchedTypes(const void* closure, upb::Handlers* h_ptr) {
 
 void RegisterMismatchedTypes2(const void* closure, upb::Handlers* h_ptr) {
   upb::HandlersPtr h(h_ptr);
+  UPB_UNUSED(closure);
 
   upb::MessageDefPtr md(h.message_def());
   ASSERT(md);
@@ -941,7 +943,7 @@ void TestArena() {
 
 extern "C" {
 
-int run_tests(int argc, char *argv[]) {
+int run_tests() {
   TestHandler<ValueTesterInt32VoidFunctionNoHandlerData>();
   TestHandler<ValueTesterInt32BoolFunctionNoHandlerData>();
   TestHandler<ValueTesterInt32VoidMethodNoHandlerData>();
diff --git a/tests/test_util.h b/tests/test_util.h
index 485410082d..418a9d8899 100644
--- a/tests/test_util.h
+++ b/tests/test_util.h
@@ -102,7 +102,7 @@ class VerboseParserEnvironment {
 
   bool ParseBuffer(int bytes) {
     if (bytes < 0) {
-      bytes = len_ - ofs_;
+      bytes = (int)(len_ - ofs_);
     }
 
     ASSERT((size_t)bytes <= (len_ - ofs_));
@@ -130,7 +130,7 @@ class VerboseParserEnvironment {
               (unsigned)bytes, (unsigned)ofs_, (unsigned)(ofs_ + bytes));
     }
 
-    int parsed = sink_.PutBuffer(subc_, buf2, bytes, &global_handle);
+    int parsed = (int)sink_.PutBuffer(subc_, buf2, bytes, &global_handle);
     free(buf2);
 
     if (verbose_) {
@@ -156,7 +156,7 @@ class VerboseParserEnvironment {
     }
 
     if (parsed > bytes && skip_until_ >= 0) {
-      skip_until_ = ofs_ + parsed;
+      skip_until_ = (int)(ofs_ + parsed);
     }
 
     ofs_ += UPB_MIN(parsed, bytes);
diff --git a/upb/bindings/lua/upbc.cc b/upb/bindings/lua/upbc.cc
index e7563bc0ba..c3988f6519 100644
--- a/upb/bindings/lua/upbc.cc
+++ b/upb/bindings/lua/upbc.cc
@@ -73,9 +73,9 @@ static void PrintString(int max_cols, absl::string_view* str,
 
 bool LuaGenerator::Generate(
     const protobuf::FileDescriptor* file,
-    const std::string& parameter,
+    const std::string& /* parameter */,
     protoc::GeneratorContext* context,
-    std::string* error) const {
+    std::string* /* error */) const {
   std::string filename = Filename(file);
   protobuf::io::ZeroCopyOutputStream* out = context->Open(filename);
   protobuf::io::Printer printer(out, '$');
diff --git a/upb/decode.c b/upb/decode.c
index 7ee199f51a..cecd68a8e7 100644
--- a/upb/decode.c
+++ b/upb/decode.c
@@ -155,7 +155,7 @@ static const char *decode_msg(upb_decstate *d, const char *ptr, upb_msg *msg,
 
 UPB_NORETURN static void decode_err(upb_decstate *d) { longjmp(d->err, 1); }
 
-static bool decode_reserve(upb_decstate *d, upb_array *arr, int elem) {
+static bool decode_reserve(upb_decstate *d, upb_array *arr, size_t elem) {
   bool need_realloc = arr->size - arr->len < elem;
   if (need_realloc && !_upb_array_realloc(arr, arr->len + elem, d->arena)) {
     decode_err(d);
@@ -324,7 +324,7 @@ static const char *decode_toarray(upb_decstate *d, const char *ptr,
       /* Fixed packed. */
       int lg2 = op - OP_FIXPCK_LG2(0);
       int mask = (1 << lg2) - 1;
-      int count = val.str_val.size >> lg2;
+      size_t count = val.str_val.size >> lg2;
       if ((val.str_val.size & mask) != 0) {
         decode_err(d); /* Length isn't a round multiple of elem size. */
       }
@@ -408,7 +408,7 @@ static const char *decode_tomsg(upb_decstate *d, const char *ptr, upb_msg *msg,
   /* Set presence if necessary. */
   if (field->presence < 0) {
     /* Oneof case */
-    int32_t *oneof_case = _upb_oneofcase_field(msg, field);
+    uint32_t *oneof_case = _upb_oneofcase_field(msg, field);
     if (op == OP_SUBMSG && *oneof_case != field->number) {
       memset(mem, 0, sizeof(void*));
     }
diff --git a/upb/def.c b/upb/def.c
index 20b2be9969..10f6b94bf1 100644
--- a/upb/def.c
+++ b/upb/def.c
@@ -1909,11 +1909,11 @@ static bool build_filedef(
   }
 
   /* Now that all names are in the table, build layouts and resolve refs. */
-  for (i = 0; i < file->ext_count; i++) {
+  for (i = 0; i < (size_t)file->ext_count; i++) {
     CHK(resolve_fielddef(ctx, file->package, (upb_fielddef*)&file->exts[i]));
   }
 
-  for (i = 0; i < file->msg_count; i++) {
+  for (i = 0; i < (size_t)file->msg_count; i++) {
     const upb_msgdef *m = &file->msgs[i];
     int j;
     for (j = 0; j < m->field_count; j++) {
@@ -1922,7 +1922,7 @@ static bool build_filedef(
   }
 
   if (!ctx->layouts) {
-    for (i = 0; i < file->msg_count; i++) {
+    for (i = 0; i < (size_t)file->msg_count; i++) {
       const upb_msgdef *m = &file->msgs[i];
       make_layout(ctx->symtab, m);
     }
@@ -1931,8 +1931,7 @@ static bool build_filedef(
   return true;
  }
 
-static bool upb_symtab_addtotabs(upb_symtab *s, symtab_addctx *ctx,
-                                 upb_status *status) {
+static bool upb_symtab_addtotabs(upb_symtab *s, symtab_addctx *ctx) {
   const upb_filedef *file = ctx->file;
   upb_alloc *alloc = upb_arena_alloc(s->arena);
   upb_strtable_iter iter;
@@ -2075,10 +2074,8 @@ static const upb_filedef *_upb_symtab_addfile(
   ctx.layouts = layouts;
   ctx.status = status;
 
-  ok = file &&
-      upb_strtable_init2(&addtab, UPB_CTYPE_CONSTPTR, ctx.tmp) &&
-      build_filedef(&ctx, file, file_proto) &&
-      upb_symtab_addtotabs(s, &ctx, status);
+  ok = file && upb_strtable_init2(&addtab, UPB_CTYPE_CONSTPTR, ctx.tmp) &&
+       build_filedef(&ctx, file, file_proto) && upb_symtab_addtotabs(s, &ctx);
 
   upb_arena_free(tmparena);
   return ok ? file : NULL;
diff --git a/upb/handlers.c b/upb/handlers.c
index 5cf7ccc074..b90b32c71f 100644
--- a/upb/handlers.c
+++ b/upb/handlers.c
@@ -152,28 +152,6 @@ const void *effective_closure_type(upb_handlers *h, const upb_fielddef *f,
   return ret;
 }
 
-/* Checks whether the START* handler specified by f & type is missing even
- * though it is required to convert the established type of an outer frame
- * ("closure_type") into the established type of an inner frame (represented in
- * the return closure type of this handler's attr. */
-bool checkstart(upb_handlers *h, const upb_fielddef *f, upb_handlertype_t type,
-                upb_status *status) {
-  const void *closure_type;
-  const upb_handlerattr *attr;
-  const void *return_closure_type;
-
-  upb_selector_t sel = handlers_getsel(h, f, type);
-  if (h->table[sel].func) return true;
-  closure_type = effective_closure_type(h, f, type);
-  attr = &h->table[sel].attr;
-  return_closure_type = attr->return_closure_type;
-  if (closure_type && return_closure_type &&
-      closure_type != return_closure_type) {
-    return false;
-  }
-  return true;
-}
-
 static upb_handlers *upb_handlers_new(const upb_msgdef *md,
                                       upb_handlercache *cache,
                                       upb_arena *arena) {
diff --git a/upb/json/parser.rl b/upb/json/parser.rl
index d5ffb65425..f1ea076281 100644
--- a/upb/json/parser.rl
+++ b/upb/json/parser.rl
@@ -975,6 +975,7 @@ static bool parse_number_from_buffer(upb_json_parser *p, const char *buf,
         upb_sink_putint32(p->top->sink, parser_getsel(p), (int32_t)val);
         return true;
       }
+      UPB_UNREACHABLE();
     }
     case UPB_TYPE_UINT32: {
       unsigned long val = strtoul(buf, &end, 0);
@@ -986,6 +987,7 @@ static bool parse_number_from_buffer(upb_json_parser *p, const char *buf,
         upb_sink_putuint32(p->top->sink, parser_getsel(p), (uint32_t)val);
         return true;
       }
+      UPB_UNREACHABLE();
     }
     /* XXX: We can't handle [u]int64 properly on 32-bit machines because
      * strto[u]ll isn't in C89. */
@@ -997,6 +999,7 @@ static bool parse_number_from_buffer(upb_json_parser *p, const char *buf,
         upb_sink_putint64(p->top->sink, parser_getsel(p), val);
         return true;
       }
+      UPB_UNREACHABLE();
     }
     case UPB_TYPE_UINT64: {
       unsigned long val = strtoul(p->accumulated, &end, 0);
@@ -1008,6 +1011,7 @@ static bool parse_number_from_buffer(upb_json_parser *p, const char *buf,
         upb_sink_putuint64(p->top->sink, parser_getsel(p), val);
         return true;
       }
+      UPB_UNREACHABLE();
     }
     default:
       break;
diff --git a/upb/json_decode.c b/upb/json_decode.c
index dd8e58254f..301f16a145 100644
--- a/upb/json_decode.c
+++ b/upb/json_decode.c
@@ -4,6 +4,7 @@
 #include <errno.h>
 #include <float.h>
 #include <inttypes.h>
+#include <limits.h>
 #include <setjmp.h>
 #include <stdlib.h>
 #include <string.h>
@@ -83,8 +84,9 @@ static bool jsondec_tryparsech(jsondec *d, char ch) {
 }
 
 static void jsondec_parselit(jsondec *d, const char *lit) {
+  size_t avail = d->end - d->ptr;
   size_t len = strlen(lit);
-  if (d->end - d->ptr < len || memcmp(d->ptr, lit, len) != 0) {
+  if (avail < len || memcmp(d->ptr, lit, len) != 0) {
     jsondec_errf(d, "Expected: '%s'", lit);
   }
   d->ptr += len;
@@ -677,7 +679,7 @@ static upb_msgval jsondec_int(jsondec *d, const upb_fielddef *f) {
     if (val.int64_val > INT32_MAX || val.int64_val < INT32_MIN) {
       jsondec_err(d, "Integer out of range.");
     }
-    val.int32_val = val.int64_val;
+    val.int32_val = (int32_t)val.int64_val;
   }
 
   return val;
@@ -713,7 +715,7 @@ static upb_msgval jsondec_uint(jsondec *d, const upb_fielddef *f) {
     if (val.uint64_val > UINT32_MAX) {
       jsondec_err(d, "Integer out of range.");
     }
-    val.uint32_val = val.uint64_val;
+    val.uint32_val = (uint32_t)val.uint64_val;
   }
 
   return val;
@@ -960,15 +962,17 @@ static int jsondec_tsdigits(jsondec *d, const char **ptr, size_t digits,
   const char *end = p + digits;
   size_t after_len = after ? strlen(after) : 0;
 
-  assert(digits <= 9);  /* int can't overflow. */
+  UPB_ASSERT(digits <= 9);  /* int can't overflow. */
 
   if (jsondec_buftouint64(d, p, end, &val) != end ||
       (after_len && memcmp(end, after, after_len) != 0)) {
     jsondec_err(d, "Malformed timestamp");
   }
 
+  UPB_ASSERT(val < INT_MAX);
+
   *ptr = end + after_len;
-  return val;
+  return (int)val;
 }
 
 static int jsondec_nanos(jsondec *d, const char **ptr, const char *end) {
@@ -977,7 +981,7 @@ static int jsondec_nanos(jsondec *d, const char **ptr, const char *end) {
 
   if (p != end && *p == '.') {
     const char *nano_end = jsondec_buftouint64(d, p + 1, end, &nanos);
-    int digits = nano_end - p - 1;
+    int digits = (int)(nano_end - p - 1);
     int exp_lg10 = 9 - digits;
     if (digits > 9) {
       jsondec_err(d, "Too many digits for partial seconds");
@@ -986,14 +990,16 @@ static int jsondec_nanos(jsondec *d, const char **ptr, const char *end) {
     *ptr = nano_end;
   }
 
-  return nanos;
+  UPB_ASSERT(nanos < INT_MAX);
+
+  return (int)nanos;
 }
 
 /* jsondec_epochdays(1970, 1, 1) == 1970-01-01 == 0. */
 int jsondec_epochdays(int y, int m, int d) {
   const uint32_t year_base = 4800;    /* Before min year, multiple of 400. */
   const uint32_t m_adj = m - 3;       /* March-based month. */
-  const uint32_t carry = m_adj > m ? 1 : 0;
+  const uint32_t carry = m_adj > (uint32_t)m ? 1 : 0;
   const uint32_t adjust = carry ? 12 : 0;
   const uint32_t y_adj = y + year_base - carry;
   const uint32_t month_days = ((m_adj + adjust) * 62719 + 769) / 2048;
@@ -1038,7 +1044,7 @@ static void jsondec_timestamp(jsondec *d, upb_msg *msg, const upb_msgdef *m) {
     switch (*ptr++) {
       case '-':
         neg = true;
-        /* Fallthrough intended. */
+        /* fallthrough */
       case '+':
         if ((end - ptr) != 5) goto malformed;
         ofs = jsondec_tsdigits(d, &ptr, 2, ":00");
diff --git a/upb/json_encode.c b/upb/json_encode.c
index 4bd9b599d9..21f661f8f6 100644
--- a/upb/json_encode.c
+++ b/upb/json_encode.c
@@ -117,7 +117,7 @@ static void jsonenc_timestamp(jsonenc *e, const upb_msg *msg,
    * Fliegel, H. F., and Van Flandern, T. C., "A Machine Algorithm for
    *   Processing Calendar Dates," Communications of the Association of
    *   Computing Machines, vol. 11 (1968), p. 657.  */
-  L = (seconds / 86400) + 68569 + 2440588;
+  L = (int)(seconds / 86400) + 68569 + 2440588;
   N = 4 * L / 146097;
   L = L - (146097 * N + 3) / 4;
   I = 4000 * (L + 1) / 1461001;
diff --git a/upb/msg.h b/upb/msg.h
index 66f04a0e80..1ded2cf3e2 100644
--- a/upb/msg.h
+++ b/upb/msg.h
@@ -40,10 +40,10 @@ enum {
 typedef struct {
   uint32_t number;
   uint16_t offset;
-  int16_t presence;      /* If >0, hasbit_index.  If <0, ~oneof_index. */
+  int16_t presence;       /* If >0, hasbit_index.  If <0, ~oneof_index. */
   uint16_t submsg_index;  /* undefined if descriptortype != MESSAGE or GROUP. */
   uint8_t descriptortype;
-  uint8_t label;
+  uint8_t label;          /* google.protobuf.Label or _UPB_LABEL_* above. */
 } upb_msglayout_field;
 
 typedef struct upb_msglayout {
@@ -131,12 +131,12 @@ UPB_INLINE void _upb_clearhas_field(const upb_msg *msg,
 
 /** Oneof case access *********************************************************/
 
-UPB_INLINE int32_t *_upb_oneofcase(upb_msg *msg, size_t case_ofs) {
-  return PTR_AT(msg, case_ofs, int32_t);
+UPB_INLINE uint32_t *_upb_oneofcase(upb_msg *msg, size_t case_ofs) {
+  return PTR_AT(msg, case_ofs, uint32_t);
 }
 
-UPB_INLINE int32_t _upb_getoneofcase(const void *msg, size_t case_ofs) {
-  return *PTR_AT(msg, case_ofs, int32_t);
+UPB_INLINE uint32_t _upb_getoneofcase(const void *msg, size_t case_ofs) {
+  return *PTR_AT(msg, case_ofs, uint32_t);
 }
 
 UPB_INLINE size_t _upb_oneofcase_ofs(const upb_msglayout_field *f) {
@@ -144,13 +144,13 @@ UPB_INLINE size_t _upb_oneofcase_ofs(const upb_msglayout_field *f) {
   return ~(int64_t)f->presence;
 }
 
-UPB_INLINE int32_t *_upb_oneofcase_field(upb_msg *msg,
-                                         const upb_msglayout_field *f) {
+UPB_INLINE uint32_t *_upb_oneofcase_field(upb_msg *msg,
+                                          const upb_msglayout_field *f) {
   return _upb_oneofcase(msg, _upb_oneofcase_ofs(f));
 }
 
-UPB_INLINE int32_t _upb_getoneofcase_field(const upb_msg *msg,
-                                           const upb_msglayout_field *f) {
+UPB_INLINE uint32_t _upb_getoneofcase_field(const upb_msg *msg,
+                                            const upb_msglayout_field *f) {
   return _upb_getoneofcase(msg, _upb_oneofcase_ofs(f));
 }
 
@@ -162,6 +162,10 @@ UPB_INLINE bool _upb_isrepeated(const upb_msglayout_field *field) {
   return (field->label & 3) == UPB_LABEL_REPEATED;
 }
 
+UPB_INLINE bool _upb_repeated_or_map(const upb_msglayout_field *field) {
+  return field->label >= UPB_LABEL_REPEATED;
+}
+
 /** upb_array *****************************************************************/
 
 /* Our internal representation for repeated fields.  */
diff --git a/upb/pb/decoder.h b/upb/pb/decoder.h
index 709db49e96..8c4d8bf5d5 100644
--- a/upb/pb/decoder.h
+++ b/upb/pb/decoder.h
@@ -158,7 +158,9 @@ class upb::pb::DecoderPtr {
    * Setting the limit will fail if the parser is currently suspended at a depth
    * greater than this, or if memory allocation of the stack fails. */
   size_t max_nesting() { return upb_pbdecoder_maxnesting(ptr()); }
-  bool set_max_nesting(size_t max) { return upb_pbdecoder_maxnesting(ptr()); }
+  bool set_max_nesting(size_t max) {
+    return upb_pbdecoder_setmaxnesting(ptr(), max);
+  }
 
   void Reset() { upb_pbdecoder_reset(ptr()); }
 
diff --git a/upb/reflection.c b/upb/reflection.c
index 057da629cc..487241b2b5 100644
--- a/upb/reflection.c
+++ b/upb/reflection.c
@@ -7,27 +7,30 @@
 
 #include "upb/port_def.inc"
 
-static char field_size[] = {
-  0,/* 0 */
-  8, /* UPB_DESCRIPTOR_TYPE_DOUBLE */
-  4, /* UPB_DESCRIPTOR_TYPE_FLOAT */
-  8, /* UPB_DESCRIPTOR_TYPE_INT64 */
-  8, /* UPB_DESCRIPTOR_TYPE_UINT64 */
-  4, /* UPB_DESCRIPTOR_TYPE_INT32 */
-  8, /* UPB_DESCRIPTOR_TYPE_FIXED64 */
-  4, /* UPB_DESCRIPTOR_TYPE_FIXED32 */
-  1, /* UPB_DESCRIPTOR_TYPE_BOOL */
-  sizeof(upb_strview), /* UPB_DESCRIPTOR_TYPE_STRING */
-  sizeof(void*), /* UPB_DESCRIPTOR_TYPE_GROUP */
-  sizeof(void*), /* UPB_DESCRIPTOR_TYPE_MESSAGE */
-  sizeof(upb_strview), /* UPB_DESCRIPTOR_TYPE_BYTES */
-  4, /* UPB_DESCRIPTOR_TYPE_UINT32 */
-  4, /* UPB_DESCRIPTOR_TYPE_ENUM */
-  4, /* UPB_DESCRIPTOR_TYPE_SFIXED32 */
-  8, /* UPB_DESCRIPTOR_TYPE_SFIXED64 */
-  4, /* UPB_DESCRIPTOR_TYPE_SINT32 */
-  8, /* UPB_DESCRIPTOR_TYPE_SINT64 */
-};
+static size_t get_field_size(const upb_msglayout_field *f) {
+  static unsigned char sizes[] = {
+    0,/* 0 */
+    8, /* UPB_DESCRIPTOR_TYPE_DOUBLE */
+    4, /* UPB_DESCRIPTOR_TYPE_FLOAT */
+    8, /* UPB_DESCRIPTOR_TYPE_INT64 */
+    8, /* UPB_DESCRIPTOR_TYPE_UINT64 */
+    4, /* UPB_DESCRIPTOR_TYPE_INT32 */
+    8, /* UPB_DESCRIPTOR_TYPE_FIXED64 */
+    4, /* UPB_DESCRIPTOR_TYPE_FIXED32 */
+    1, /* UPB_DESCRIPTOR_TYPE_BOOL */
+    sizeof(upb_strview), /* UPB_DESCRIPTOR_TYPE_STRING */
+    sizeof(void*), /* UPB_DESCRIPTOR_TYPE_GROUP */
+    sizeof(void*), /* UPB_DESCRIPTOR_TYPE_MESSAGE */
+    sizeof(upb_strview), /* UPB_DESCRIPTOR_TYPE_BYTES */
+    4, /* UPB_DESCRIPTOR_TYPE_UINT32 */
+    4, /* UPB_DESCRIPTOR_TYPE_ENUM */
+    4, /* UPB_DESCRIPTOR_TYPE_SFIXED32 */
+    8, /* UPB_DESCRIPTOR_TYPE_SFIXED64 */
+    4, /* UPB_DESCRIPTOR_TYPE_SINT32 */
+    8, /* UPB_DESCRIPTOR_TYPE_SINT64 */
+  };
+  return _upb_repeated_or_map(f) ? sizeof(void *) : sizes[f->descriptortype];
+}
 
 /* Strings/bytes are special-cased in maps. */
 static char _upb_fieldtype_to_mapsize[12] = {
@@ -59,9 +62,7 @@ static upb_msgval _upb_msg_getraw(const upb_msg *msg, const upb_fielddef *f) {
   const upb_msglayout_field *field = upb_fielddef_layout(f);
   const char *mem = UPB_PTR_AT(msg, field->offset, char);
   upb_msgval val = {0};
-  int size = upb_fielddef_isseq(f) ? sizeof(void *)
-                                   : field_size[field->descriptortype];
-  memcpy(&val, mem, size);
+  memcpy(&val, mem, get_field_size(field));
   return val;
 }
 
@@ -175,9 +176,8 @@ void upb_msg_set(upb_msg *msg, const upb_fielddef *f, upb_msgval val,
                  upb_arena *a) {
   const upb_msglayout_field *field = upb_fielddef_layout(f);
   char *mem = UPB_PTR_AT(msg, field->offset, char);
-  int size = upb_fielddef_isseq(f) ? sizeof(void *)
-                                   : field_size[field->descriptortype];
-  memcpy(mem, &val, size);
+  UPB_UNUSED(a);  /* We reserve the right to make set insert into a map. */
+  memcpy(mem, &val, get_field_size(field));
   if (field->presence > 0) {
     _upb_sethas_field(msg, field);
   } else if (in_oneof(field)) {
@@ -188,18 +188,16 @@ void upb_msg_set(upb_msg *msg, const upb_fielddef *f, upb_msgval val,
 void upb_msg_clearfield(upb_msg *msg, const upb_fielddef *f) {
   const upb_msglayout_field *field = upb_fielddef_layout(f);
   char *mem = UPB_PTR_AT(msg, field->offset, char);
-  int size = upb_fielddef_isseq(f) ? sizeof(void *)
-                                   : field_size[field->descriptortype];
 
   if (field->presence > 0) {
     _upb_clearhas_field(msg, field);
   } else if (in_oneof(field)) {
-    int32_t *oneof_case = _upb_oneofcase_field(msg, field);
+    uint32_t *oneof_case = _upb_oneofcase_field(msg, field);
     if (*oneof_case != field->number) return;
     *oneof_case = 0;
   }
 
-  memset(mem, 0, size);
+  memset(mem, 0, get_field_size(field));
 }
 
 void upb_msg_clear(upb_msg *msg, const upb_msgdef *m) {
@@ -212,6 +210,7 @@ bool upb_msg_next(const upb_msg *msg, const upb_msgdef *m,
   size_t i = *iter;
   const upb_msgval zero = {0};
   const upb_fielddef *f;
+  UPB_UNUSED(ext_pool);
   while ((f = _upb_msgdef_field(m, (int)++i)) != NULL) {
     upb_msgval val = _upb_msg_getraw(msg, f);
 
diff --git a/upb/table.c b/upb/table.c
index 084b6a2bbf..e89f72c698 100644
--- a/upb/table.c
+++ b/upb/table.c
@@ -281,6 +281,7 @@ static bool streql(upb_tabkey k1, lookupkey_t k2) {
 }
 
 bool upb_strtable_init2(upb_strtable *t, upb_ctype_t ctype, upb_alloc *a) {
+  UPB_UNUSED(ctype);  /* TODO(haberman): rm */
   return init(&t->t, 2, a);
 }
 
@@ -473,6 +474,7 @@ bool upb_inttable_sizedinit(upb_inttable *t, size_t asize, int hsize_lg2,
 }
 
 bool upb_inttable_init2(upb_inttable *t, upb_ctype_t ctype, upb_alloc *a) {
+  UPB_UNUSED(ctype);  /* TODO(haberman): rm */
   return upb_inttable_sizedinit(t, 0, 4, a);
 }
 
@@ -786,8 +788,8 @@ uint32_t upb_murmur_hash2(const void * key, size_t len, uint32_t seed) {
     int32_t sr;
 
     switch(align) {
-      case 1: t |= data[2] << 16;
-      case 2: t |= data[1] << 8;
+      case 1: t |= data[2] << 16;  /* fallthrough */
+      case 2: t |= data[1] << 8;   /* fallthrough */
       case 3: t |= data[0];
     }
 
@@ -825,9 +827,9 @@ uint32_t upb_murmur_hash2(const void * key, size_t len, uint32_t seed) {
       uint32_t k;
 
       switch(align) {
-        case 3: d |= data[2] << 16;
-        case 2: d |= data[1] << 8;
-        case 1: d |= data[0];
+        case 3: d |= data[2] << 16;  /* fallthrough */
+        case 2: d |= data[1] << 8;   /* fallthrough */
+        case 1: d |= data[0];        /* fallthrough */
       }
 
       k = (t >> sr) | (d << sl);
@@ -840,15 +842,15 @@ uint32_t upb_murmur_hash2(const void * key, size_t len, uint32_t seed) {
        * Handle tail bytes */
 
       switch(len) {
-        case 3: h ^= data[2] << 16;
-        case 2: h ^= data[1] << 8;
-        case 1: h ^= data[0]; h *= m;
+        case 3: h ^= data[2] << 16;    /* fallthrough */
+        case 2: h ^= data[1] << 8;     /* fallthrough */
+        case 1: h ^= data[0]; h *= m;  /* fallthrough */
       };
     } else {
       switch(len) {
-        case 3: d |= data[2] << 16;
-        case 2: d |= data[1] << 8;
-        case 1: d |= data[0];
+        case 3: d |= data[2] << 16;  /* fallthrough */
+        case 2: d |= data[1] << 8;   /* fallthrough */
+        case 1: d |= data[0];        /* fallthrough */
         case 0: h ^= (t >> sr) | (d << sl); h *= m;
       }
     }
@@ -872,8 +874,8 @@ uint32_t upb_murmur_hash2(const void * key, size_t len, uint32_t seed) {
      * Handle tail bytes */
 
     switch(len) {
-      case 3: h ^= data[2] << 16;
-      case 2: h ^= data[1] << 8;
+      case 3: h ^= data[2] << 16; /* fallthrough */
+      case 2: h ^= data[1] << 8;  /* fallthrough */
       case 1: h ^= data[0]; h *= m;
     };
 
diff --git a/upb/text_encode.c b/upb/text_encode.c
index 3ebd9cff74..7c99228131 100644
--- a/upb/text_encode.c
+++ b/upb/text_encode.c
@@ -263,7 +263,7 @@ static const char *txtenc_unknown(txtenc *e, const char *ptr, const char *end,
     tag = (uint32_t)tag_64;
 
     if ((tag & 7) == UPB_WIRE_TYPE_END_GROUP) {
-      CHK((tag >> 3) == groupnum);
+      CHK((tag >> 3) == (uint32_t)groupnum);
       return ptr;
     }
 
@@ -295,10 +295,11 @@ static const char *txtenc_unknown(txtenc *e, const char *ptr, const char *end,
       }
       case UPB_WIRE_TYPE_DELIMITED: {
         uint64_t len;
+        size_t avail = end - ptr;
         char *start = e->ptr;
         size_t start_overflow = e->overflow;
         CHK(ptr = txtenc_parsevarint(ptr, end, &len));
-        CHK(end - ptr >= len);
+        CHK(avail >= len);
 
         /* Speculatively try to parse as message. */
         txtenc_putstr(e, "{");
@@ -310,10 +311,12 @@ static const char *txtenc_unknown(txtenc *e, const char *ptr, const char *end,
           txtenc_putstr(e, "}");
         } else {
           /* Didn't work out, print as raw bytes. */
+          upb_strview str;
           e->indent_depth--;
           e->ptr = start;
           e->overflow = start_overflow;
-          upb_strview str = {ptr, len};
+          str.data = ptr;
+          str.size = len;
           txtenc_string(e, str, true);
         }
         ptr += len;
diff --git a/upb/upb.c b/upb/upb.c
index 84852f49a6..c2d406950d 100644
--- a/upb/upb.c
+++ b/upb/upb.c
@@ -110,10 +110,10 @@ static void upb_arena_addblock(upb_arena *a, void *ptr, size_t size) {
   mem_block *block = ptr;
 
   block->next = a->freelist;
-  block->size = size;
+  block->size = (uint32_t)size;
   block->cleanups = 0;
   a->freelist = block;
-  a->last_size = size;
+  a->last_size = block->size;
   if (!a->freelist_tail) a->freelist_tail = block;
 
   a->head.ptr = UPB_PTR_AT(block, memblock_reserve, char);
diff --git a/upb/upb.h b/upb/upb.h
index 19ee059b8f..c3e1c5f3d5 100644
--- a/upb/upb.h
+++ b/upb/upb.h
@@ -271,7 +271,7 @@ typedef enum {
   UPB_DTYPE_SINT64   = 18
 } upb_descriptortype_t;
 
-#define UPB_MAP_BEGIN -1
+#define UPB_MAP_BEGIN ((size_t)-1)
 
 #include "upb/port_undef.inc"
 
diff --git a/upbc/generator.cc b/upbc/generator.cc
index af39cacd12..d5c27fb2af 100644
--- a/upbc/generator.cc
+++ b/upbc/generator.cc
@@ -43,7 +43,7 @@ static std::string DefSourceFilename(std::string proto_filename) {
 class Output {
  public:
   Output(protobuf::io::ZeroCopyOutputStream* stream) : stream_(stream) {}
-  ~Output() { stream_->BackUp(size_); }
+  ~Output() { stream_->BackUp((int)size_); }
 
   template <class... Arg>
   void operator()(absl::string_view format, const Arg&... arg) {
@@ -922,9 +922,9 @@ void WriteDefSource(const protobuf::FileDescriptor* file, Output& output) {
 }
 
 bool Generator::Generate(const protobuf::FileDescriptor* file,
-                         const std::string& parameter,
+                         const std::string& /* parameter */,
                          protoc::GeneratorContext* context,
-                         std::string* error) const {
+                         std::string* /* error */) const {
   Output h_output(context->Open(HeaderFilename(file->name())));
   WriteHeader(file, h_output);