diff --git a/tests/conformance_upb.c b/tests/conformance_upb.c
index 9f83e807e4..1671409f61 100644
--- a/tests/conformance_upb.c
+++ b/tests/conformance_upb.c
@@ -81,7 +81,7 @@ void DoTest(
       char *serialized = protobuf_test_messages_proto3_TestAllTypes_serialize(
           test_message, env, &serialized_len);
       if (!serialized) {
-        fprintf(stderr, "conformance_upb: Error serialiing.");
+        fprintf(stderr, "conformance_upb: Error serializing.");
         exit(1);
       }
       conformance_ConformanceResponse_set_protobuf_payload(
diff --git a/tools/make_c_api.lua b/tools/make_c_api.lua
index aaf5d1ead4..c13f37c413 100644
--- a/tools/make_c_api.lua
+++ b/tools/make_c_api.lua
@@ -30,11 +30,6 @@ function strip_proto(filename)
   return string.gsub(filename, '%.proto$','')
 end
 
---[[
-  [upb.TYPE_ENUM]     = 5,
-  [upb.TYPE_MESSAGE]  = 8,
---]]
-
 local function join(...)
   return table.concat({...}, ".")
 end
@@ -138,6 +133,12 @@ local function field_layout_rank(field)
   --   5. string fields
   --   6. submessage fields
   --   7. repeated fields
+  --
+  -- This has the following nice properties:
+  --
+  --  1. padding alignment is (nearly) minimized.
+  --  2. fields that might have defaults (1-5) are segregated
+  --     from fields that are always zero-initialized (6-7).
   local rank
   if field:containing_oneof() then
     rank = 4
diff --git a/tools/upbc.lua b/tools/upbc.lua
index bf9a68d36a..bfd93f86ab 100644
--- a/tools/upbc.lua
+++ b/tools/upbc.lua
@@ -18,6 +18,10 @@ for _, argument in ipairs(arg) do
   if argument == "--generate-upbdefs" then
     generate_upbdefs = true
   else
+    if src then
+      print("upbc can only handle one input file at a time.")
+      return 1
+    end
     src = argument
   end
 end
diff --git a/upb/msg.c b/upb/msg.c
index 34525b78e8..f1070d72fe 100644
--- a/upb/msg.c
+++ b/upb/msg.c
@@ -340,8 +340,8 @@ static upb_msglayout *upb_msglayout_new(const upb_msgdef *m) {
   }
 
   /* Size of the entire structure should be a multiple of its greatest
-   * alignment. */
-  l->data.size = align_up(l->data.size, 8 /* TODO: track for real? */);
+   * alignment.  TODO: track overall alignment for real? */
+  l->data.size = align_up(l->data.size, 8);
 
   if (upb_msglayout_initdefault(l, m)) {
     return l;
diff --git a/upb/msg.h b/upb/msg.h
index ee1e2fbd10..7026a50edb 100644
--- a/upb/msg.h
+++ b/upb/msg.h
@@ -408,7 +408,7 @@ typedef struct upb_msglayout_msginit_v1 {
   const upb_msglayout_oneofinit_v1 *oneofs;
   void *default_msg;
   /* Must be aligned to sizeof(void*).  Doesn't include internal members like
-   * unknown * fields, extension dict, pointer to msglayout, etc. */
+   * unknown fields, extension dict, pointer to msglayout, etc. */
   uint32_t size;
   uint16_t field_count;
   uint16_t oneof_count;