diff --git a/generated_for_cmake/upb/json/parser.c b/generated_for_cmake/upb/json/parser.c
index 5445fa62a3..ca018f4c0f 100644
--- a/generated_for_cmake/upb/json/parser.c
+++ b/generated_for_cmake/upb/json/parser.c
@@ -1372,7 +1372,12 @@ static bool end_stringval_nontop(upb_json_parser *p) {
         upb_selector_t sel = parser_getsel(p);
         upb_sink_putint32(p->top->sink, sel, int_val);
       } else {
-        upb_status_seterrf(p->status, "Enum value unknown: '%.*s'", len, buf);
+        if (p->ignore_json_unknown) {
+          ok = true;
+          /* TODO(teboring): Should also clean this field. */
+        } else {
+          upb_status_seterrf(p->status, "Enum value unknown: '%.*s'", len, buf);
+        }
       }
 
       break;
@@ -2577,11 +2582,11 @@ static bool does_fieldmask_end(upb_json_parser *p) {
  * final state once, when the closing '"' is seen. */
 
 
-#line 2782 "upb/json/parser.rl"
+#line 2787 "upb/json/parser.rl"
 
 
 
-#line 2585 "upb/json/parser.c"
+#line 2590 "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, 
@@ -2836,7 +2841,7 @@ static const int json_en_value_machine = 78;
 static const int json_en_main = 1;
 
 
-#line 2785 "upb/json/parser.rl"
+#line 2790 "upb/json/parser.rl"
 
 size_t parse(void *closure, const void *hd, const char *buf, size_t size,
              const upb_bufhandle *handle) {
@@ -2859,7 +2864,7 @@ size_t parse(void *closure, const void *hd, const char *buf, size_t size,
   capture_resume(parser, buf);
 
   
-#line 2863 "upb/json/parser.c"
+#line 2868 "upb/json/parser.c"
 	{
 	int _klen;
 	unsigned int _trans;
@@ -2934,147 +2939,147 @@ _match:
 		switch ( *_acts++ )
 		{
 	case 1:
-#line 2590 "upb/json/parser.rl"
+#line 2595 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 2:
-#line 2592 "upb/json/parser.rl"
+#line 2597 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 23;goto _again;} }
 	break;
 	case 3:
-#line 2596 "upb/json/parser.rl"
+#line 2601 "upb/json/parser.rl"
 	{ start_text(parser, p); }
 	break;
 	case 4:
-#line 2597 "upb/json/parser.rl"
+#line 2602 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_text(parser, p)); }
 	break;
 	case 5:
-#line 2603 "upb/json/parser.rl"
+#line 2608 "upb/json/parser.rl"
 	{ start_hex(parser); }
 	break;
 	case 6:
-#line 2604 "upb/json/parser.rl"
+#line 2609 "upb/json/parser.rl"
 	{ hexdigit(parser, p); }
 	break;
 	case 7:
-#line 2605 "upb/json/parser.rl"
+#line 2610 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hex(parser)); }
 	break;
 	case 8:
-#line 2611 "upb/json/parser.rl"
+#line 2616 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(escape(parser, p)); }
 	break;
 	case 9:
-#line 2617 "upb/json/parser.rl"
+#line 2622 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 10:
-#line 2622 "upb/json/parser.rl"
+#line 2627 "upb/json/parser.rl"
 	{ start_year(parser, p); }
 	break;
 	case 11:
-#line 2623 "upb/json/parser.rl"
+#line 2628 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_year(parser, p)); }
 	break;
 	case 12:
-#line 2627 "upb/json/parser.rl"
+#line 2632 "upb/json/parser.rl"
 	{ start_month(parser, p); }
 	break;
 	case 13:
-#line 2628 "upb/json/parser.rl"
+#line 2633 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_month(parser, p)); }
 	break;
 	case 14:
-#line 2632 "upb/json/parser.rl"
+#line 2637 "upb/json/parser.rl"
 	{ start_day(parser, p); }
 	break;
 	case 15:
-#line 2633 "upb/json/parser.rl"
+#line 2638 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_day(parser, p)); }
 	break;
 	case 16:
-#line 2637 "upb/json/parser.rl"
+#line 2642 "upb/json/parser.rl"
 	{ start_hour(parser, p); }
 	break;
 	case 17:
-#line 2638 "upb/json/parser.rl"
+#line 2643 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hour(parser, p)); }
 	break;
 	case 18:
-#line 2642 "upb/json/parser.rl"
+#line 2647 "upb/json/parser.rl"
 	{ start_minute(parser, p); }
 	break;
 	case 19:
-#line 2643 "upb/json/parser.rl"
+#line 2648 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_minute(parser, p)); }
 	break;
 	case 20:
-#line 2647 "upb/json/parser.rl"
+#line 2652 "upb/json/parser.rl"
 	{ start_second(parser, p); }
 	break;
 	case 21:
-#line 2648 "upb/json/parser.rl"
+#line 2653 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_second(parser, p)); }
 	break;
 	case 22:
-#line 2653 "upb/json/parser.rl"
+#line 2658 "upb/json/parser.rl"
 	{ start_duration_base(parser, p); }
 	break;
 	case 23:
-#line 2654 "upb/json/parser.rl"
+#line 2659 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_duration_base(parser, p)); }
 	break;
 	case 24:
-#line 2656 "upb/json/parser.rl"
+#line 2661 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 25:
-#line 2661 "upb/json/parser.rl"
+#line 2666 "upb/json/parser.rl"
 	{ start_timestamp_base(parser); }
 	break;
 	case 26:
-#line 2663 "upb/json/parser.rl"
+#line 2668 "upb/json/parser.rl"
 	{ start_timestamp_fraction(parser, p); }
 	break;
 	case 27:
-#line 2664 "upb/json/parser.rl"
+#line 2669 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_fraction(parser, p)); }
 	break;
 	case 28:
-#line 2666 "upb/json/parser.rl"
+#line 2671 "upb/json/parser.rl"
 	{ start_timestamp_zone(parser, p); }
 	break;
 	case 29:
-#line 2667 "upb/json/parser.rl"
+#line 2672 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_zone(parser, p)); }
 	break;
 	case 30:
-#line 2669 "upb/json/parser.rl"
+#line 2674 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 31:
-#line 2674 "upb/json/parser.rl"
+#line 2679 "upb/json/parser.rl"
 	{ start_fieldmask_path_text(parser, p); }
 	break;
 	case 32:
-#line 2675 "upb/json/parser.rl"
+#line 2680 "upb/json/parser.rl"
 	{ end_fieldmask_path_text(parser, p); }
 	break;
 	case 33:
-#line 2680 "upb/json/parser.rl"
+#line 2685 "upb/json/parser.rl"
 	{ start_fieldmask_path(parser); }
 	break;
 	case 34:
-#line 2681 "upb/json/parser.rl"
+#line 2686 "upb/json/parser.rl"
 	{ end_fieldmask_path(parser); }
 	break;
 	case 35:
-#line 2687 "upb/json/parser.rl"
+#line 2692 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 36:
-#line 2692 "upb/json/parser.rl"
+#line 2697 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_TIMESTAMP)) {
           {stack[top++] = cs; cs = 47;goto _again;}
@@ -3088,11 +3093,11 @@ _match:
       }
 	break;
 	case 37:
-#line 2705 "upb/json/parser.rl"
+#line 2710 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 78;goto _again;} }
 	break;
 	case 38:
-#line 2710 "upb/json/parser.rl"
+#line 2715 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           start_any_member(parser, p);
@@ -3102,11 +3107,11 @@ _match:
       }
 	break;
 	case 39:
-#line 2717 "upb/json/parser.rl"
+#line 2722 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_membername(parser)); }
 	break;
 	case 40:
-#line 2720 "upb/json/parser.rl"
+#line 2725 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           end_any_member(parser, p);
@@ -3116,7 +3121,7 @@ _match:
       }
 	break;
 	case 41:
-#line 2731 "upb/json/parser.rl"
+#line 2736 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           start_any_object(parser, p);
@@ -3126,7 +3131,7 @@ _match:
       }
 	break;
 	case 42:
-#line 2740 "upb/json/parser.rl"
+#line 2745 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           CHECK_RETURN_TOP(end_any_object(parser, p));
@@ -3136,54 +3141,54 @@ _match:
       }
 	break;
 	case 43:
-#line 2752 "upb/json/parser.rl"
+#line 2757 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_array(parser)); }
 	break;
 	case 44:
-#line 2756 "upb/json/parser.rl"
+#line 2761 "upb/json/parser.rl"
 	{ end_array(parser); }
 	break;
 	case 45:
-#line 2761 "upb/json/parser.rl"
+#line 2766 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_number(parser, p)); }
 	break;
 	case 46:
-#line 2762 "upb/json/parser.rl"
+#line 2767 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 47:
-#line 2764 "upb/json/parser.rl"
+#line 2769 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_stringval(parser)); }
 	break;
 	case 48:
-#line 2765 "upb/json/parser.rl"
+#line 2770 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_stringval(parser)); }
 	break;
 	case 49:
-#line 2767 "upb/json/parser.rl"
+#line 2772 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 50:
-#line 2769 "upb/json/parser.rl"
+#line 2774 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 51:
-#line 2771 "upb/json/parser.rl"
+#line 2776 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 52:
-#line 2773 "upb/json/parser.rl"
+#line 2778 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_subobject_full(parser)); }
 	break;
 	case 53:
-#line 2774 "upb/json/parser.rl"
+#line 2779 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
 	case 54:
-#line 2779 "upb/json/parser.rl"
+#line 2784 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
-#line 3187 "upb/json/parser.c"
+#line 3192 "upb/json/parser.c"
 		}
 	}
 
@@ -3200,32 +3205,32 @@ _again:
 	while ( __nacts-- > 0 ) {
 		switch ( *__acts++ ) {
 	case 0:
-#line 2588 "upb/json/parser.rl"
+#line 2593 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; 	if ( p == pe )
 		goto _test_eof;
 goto _again;} }
 	break;
 	case 46:
-#line 2762 "upb/json/parser.rl"
+#line 2767 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 49:
-#line 2767 "upb/json/parser.rl"
+#line 2772 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 50:
-#line 2769 "upb/json/parser.rl"
+#line 2774 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 51:
-#line 2771 "upb/json/parser.rl"
+#line 2776 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 53:
-#line 2774 "upb/json/parser.rl"
+#line 2779 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
-#line 3229 "upb/json/parser.c"
+#line 3234 "upb/json/parser.c"
 		}
 	}
 	}
@@ -3233,7 +3238,7 @@ goto _again;} }
 	_out: {}
 	}
 
-#line 2807 "upb/json/parser.rl"
+#line 2812 "upb/json/parser.rl"
 
   if (p != pe) {
     upb_status_seterrf(parser->status, "Parse error at '%.*s'\n", pe - p, p);
@@ -3276,13 +3281,13 @@ static void json_parser_reset(upb_json_parser *p) {
 
   /* Emit Ragel initialization of the parser. */
   
-#line 3280 "upb/json/parser.c"
+#line 3285 "upb/json/parser.c"
 	{
 	cs = json_start;
 	top = 0;
 	}
 
-#line 2849 "upb/json/parser.rl"
+#line 2854 "upb/json/parser.rl"
   p->current_state = cs;
   p->parser_top = top;
   accumulate_clear(p);
diff --git a/tests/json/test_json.cc b/tests/json/test_json.cc
index 7ff01d198a..e5f0103584 100644
--- a/tests/json/test_json.cc
+++ b/tests/json/test_json.cc
@@ -138,6 +138,21 @@ static TestCase kTestRoundtripMessagesPreserve[] = {
   TEST_SENTINEL
 };
 
+static TestCase kTestSkipUnknown[] = {
+  {
+    TEST("{\"optionalEnum\":\"UNKNOWN_ENUM_VALUE\"}"),
+    EXPECT("{}"),
+  },
+  TEST_SENTINEL
+};
+
+static TestCase kTestFailure[] = {
+  {
+    TEST("{\"optionalEnum\":\"UNKNOWN_ENUM_VALUE\"}"),
+  },
+  TEST_SENTINEL
+};
+
 class StringSink {
  public:
   StringSink() {
@@ -173,13 +188,15 @@ void test_json_roundtrip_message(const char* json_src,
                                  const char* json_expected,
                                  const upb::Handlers* serialize_handlers,
                                  const upb::json::ParserMethodPtr parser_method,
-                                 int seam) {
+                                 int seam,
+                                 bool ignore_unknown) {
   VerboseParserEnvironment env(verbose);
   StringSink data_sink;
   upb::json::PrinterPtr printer = upb::json::PrinterPtr::Create(
       env.arena(), serialize_handlers, data_sink.Sink());
   upb::json::ParserPtr parser = upb::json::ParserPtr::Create(
-      env.arena(), parser_method, NULL, printer.input(), env.status(), false);
+      env.arena(), parser_method, NULL, printer.input(),
+      env.status(), ignore_unknown);
   env.ResetBytesSink(parser.input());
   env.Reset(json_src, strlen(json_src), false, false);
 
@@ -196,8 +213,8 @@ void test_json_roundtrip_message(const char* json_src,
              data_sink.Data().size())) {
     fprintf(stderr,
             "JSON parse/serialize roundtrip result differs:\n"
-            "Original:\n%s\nParsed/Serialized:\n%s\n",
-            json_src, data_sink.Data().c_str());
+            "Expected:\n%s\nParsed/Serialized:\n%s\n",
+            json_expected, data_sink.Data().c_str());
     abort();
   }
 }
@@ -225,7 +242,23 @@ 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, i,
+                                  false);
+    }
+  }
+
+  // Tests ignore unknown.
+  for (const TestCase* test_case = kTestSkipUnknown;
+       test_case->input != NULL; test_case++) {
+    const char *expected =
+        (test_case->expected == EXPECT_SAME) ?
+        test_case->input :
+        test_case->expected;
+
+    for (size_t i = 0; i < strlen(test_case->input); i++) {
+      test_json_roundtrip_message(test_case->input, expected,
+                                  serialize_handlers, parser_method, i,
+                                  true);
     }
   }
 
@@ -241,7 +274,52 @@ 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, i,
+                                  false);
+    }
+  }
+}
+
+void test_json_parse_failure(const char* json_src,
+                             const upb::Handlers* serialize_handlers,
+                             const upb::json::ParserMethodPtr parser_method,
+                             int seam) {
+  VerboseParserEnvironment env(verbose);
+  StringSink data_sink;
+  upb::json::PrinterPtr printer = upb::json::PrinterPtr::Create(
+      env.arena(), serialize_handlers, data_sink.Sink());
+  upb::json::ParserPtr parser = upb::json::ParserPtr::Create(
+      env.arena(), parser_method, NULL, printer.input(), env.status(), false);
+  env.ResetBytesSink(parser.input());
+  env.Reset(json_src, strlen(json_src), false, true);
+
+  bool ok = env.Start() &&
+            env.ParseBuffer(seam) &&
+            env.ParseBuffer(-1) &&
+            env.End();
+
+  ASSERT(!ok);
+  ASSERT(env.CheckConsistency());
+}
+
+// Starts with a proto message in JSON format, parses and expects failre.
+void test_json_failure() {
+  upb::SymbolTable symtab;
+  upb::HandlerCache serialize_handlercache(
+      upb::json::PrinterPtr::NewCache(false));
+  upb::json::CodeCache parse_codecache;
+
+  upb::MessageDefPtr md(upb_test_json_TestMessage_getmsgdef(symtab.ptr()));
+  ASSERT(md);
+  const upb::Handlers* serialize_handlers = serialize_handlercache.Get(md);
+  const upb::json::ParserMethodPtr parser_method = parse_codecache.Get(md);
+  ASSERT(serialize_handlers);
+
+  for (const TestCase* test_case = kTestFailure;
+       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);
     }
   }
 }
@@ -251,6 +329,7 @@ int run_tests(int argc, char *argv[]) {
   UPB_UNUSED(argc);
   UPB_UNUSED(argv);
   test_json_roundtrip();
+  test_json_failure();
   return 0;
 }
 }
diff --git a/upb/json/parser.rl b/upb/json/parser.rl
index 13534706af..0f58f84b18 100644
--- a/upb/json/parser.rl
+++ b/upb/json/parser.rl
@@ -1370,7 +1370,12 @@ static bool end_stringval_nontop(upb_json_parser *p) {
         upb_selector_t sel = parser_getsel(p);
         upb_sink_putint32(p->top->sink, sel, int_val);
       } else {
-        upb_status_seterrf(p->status, "Enum value unknown: '%.*s'", len, buf);
+        if (p->ignore_json_unknown) {
+          ok = true;
+          /* TODO(teboring): Should also clean this field. */
+        } else {
+          upb_status_seterrf(p->status, "Enum value unknown: '%.*s'", len, buf);
+        }
       }
 
       break;