diff --git a/upb/alloc.h b/upb/alloc.h
index 870a1b1d9e..e6719c5731 100644
--- a/upb/alloc.h
+++ b/upb/alloc.h
@@ -89,10 +89,10 @@ UPB_INLINE void* upb_grealloc(void* ptr, size_t oldsize, size_t size) {
 
 UPB_INLINE void upb_gfree(void* ptr) { upb_free(&upb_alloc_global, ptr); }
 
-#include "upb/port_undef.inc"
-
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_ALLOC_H_ */
diff --git a/upb/arena.h b/upb/arena.h
index 1fabbf2aef..f978322db6 100644
--- a/upb/arena.h
+++ b/upb/arena.h
@@ -157,10 +157,10 @@ UPB_INLINE upb_Arena* upb_Arena_New(void) {
   return upb_Arena_Init(NULL, 0, &upb_alloc_global);
 }
 
-#include "upb/port_undef.inc"
-
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_ARENA_H_ */
diff --git a/upb/decode.h b/upb/decode.h
index 985e3e4c39..f9ad98f7c9 100644
--- a/upb/decode.h
+++ b/upb/decode.h
@@ -36,7 +36,7 @@
 #include "upb/extension_registry.h"
 #include "upb/msg.h"
 
-/* Must be last. */
+// Must be last.
 #include "upb/port_def.inc"
 
 #ifdef __cplusplus
diff --git a/upb/decode_fast.h b/upb/decode_fast.h
index b04aeedb85..3ccd1a02b1 100644
--- a/upb/decode_fast.h
+++ b/upb/decode_fast.h
@@ -64,6 +64,13 @@
 
 #include "upb/msg.h"
 
+// Must be last.
+#include "upb/port_def.inc"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct upb_Decoder;
 
 // The fallback, generic parsing function that can handle any field type.
@@ -150,4 +157,10 @@ TAGBYTES(r)
 
 #undef UPB_PARSE_PARAMS
 
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#include "upb/port_undef.inc"
+
 #endif /* UPB_DECODE_FAST_H_ */
diff --git a/upb/def.h b/upb/def.h
index 2cb312df1a..84cd2fb85b 100644
--- a/upb/def.h
+++ b/upb/def.h
@@ -32,12 +32,12 @@
 #include "upb/internal/table.h"
 #include "upb/upb.h"
 
-/* Must be last. */
+// Must be last.
 #include "upb/port_def.inc"
 
 #ifdef __cplusplus
 extern "C" {
-#endif /* __cplusplus */
+#endif
 
 struct upb_EnumDef;
 typedef struct upb_EnumDef upb_EnumDef;
@@ -407,10 +407,10 @@ UPB_INLINE bool _upb_DefPool_LoadDefInit(upb_DefPool* s,
   return _upb_DefPool_LoadDefInitEx(s, init, false);
 }
 
-#include "upb/port_undef.inc"
-
 #ifdef __cplusplus
 } /* extern "C" */
-#endif /* __cplusplus */
+#endif
+
+#include "upb/port_undef.inc"
 
 #endif /* UPB_DEF_H_ */
diff --git a/upb/encode.h b/upb/encode.h
index 791d84a74c..977baa424a 100644
--- a/upb/encode.h
+++ b/upb/encode.h
@@ -34,7 +34,7 @@
 
 #include "upb/msg.h"
 
-/* Must be last. */
+// Must be last.
 #include "upb/port_def.inc"
 
 #ifdef __cplusplus
@@ -72,10 +72,10 @@ upb_EncodeStatus upb_Encode(const void* msg, const upb_MiniTable* l,
                             int options, upb_Arena* arena, char** buf,
                             size_t* size);
 
-#include "upb/port_undef.inc"
-
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_ENCODE_H_ */
diff --git a/upb/extension_registry.h b/upb/extension_registry.h
index 0e0a4440ca..cafe6893d4 100644
--- a/upb/extension_registry.h
+++ b/upb/extension_registry.h
@@ -28,10 +28,11 @@
 #ifndef UPB_EXTENSION_REGISTRY_H_
 #define UPB_EXTENSION_REGISTRY_H_
 
-#include <stddef.h>
-
 #include "upb/upb.h"
 
+// Must be last.
+#include "upb/port_def.inc"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -81,4 +82,6 @@ upb_ExtensionRegistry* upb_ExtensionRegistry_New(upb_Arena* arena);
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_EXTENSION_REGISTRY_H_ */
diff --git a/upb/json_decode.h b/upb/json_decode.h
index 848f4df33c..c7b6839427 100644
--- a/upb/json_decode.h
+++ b/upb/json_decode.h
@@ -30,6 +30,9 @@
 
 #include "upb/def.h"
 
+// Must be last.
+#include "upb/port_def.inc"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -44,4 +47,6 @@ bool upb_JsonDecode(const char* buf, size_t size, upb_Message* msg,
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_JSONDECODE_H_ */
diff --git a/upb/json_encode.h b/upb/json_encode.h
index 6e0cac3fc1..7d83206580 100644
--- a/upb/json_encode.h
+++ b/upb/json_encode.h
@@ -30,6 +30,9 @@
 
 #include "upb/def.h"
 
+// Must be last.
+#include "upb/port_def.inc"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -62,4 +65,6 @@ size_t upb_JsonEncode(const upb_Message* msg, const upb_MessageDef* m,
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_JSONENCODE_H_ */
diff --git a/upb/msg.h b/upb/msg.h
index 89db4dd6eb..cdb5c2bd13 100644
--- a/upb/msg.h
+++ b/upb/msg.h
@@ -62,10 +62,10 @@ const char* upb_Message_GetUnknown(const upb_Message* msg, size_t* len);
 /* Returns the number of extensions present in this message. */
 size_t upb_Message_ExtensionCount(const upb_Message* msg);
 
-#include "upb/port_undef.inc"
-
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_MSG_INT_H_ */
diff --git a/upb/msg_internal.h b/upb/msg_internal.h
index 7360ad12c1..3ed032d5e0 100644
--- a/upb/msg_internal.h
+++ b/upb/msg_internal.h
@@ -35,7 +35,6 @@
 #ifndef UPB_MSG_INT_H_
 #define UPB_MSG_INT_H_
 
-#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -44,7 +43,7 @@
 #include "upb/msg.h"
 #include "upb/upb.h"
 
-/* Must be last. */
+// Must be last.
 #include "upb/port_def.inc"
 
 #ifdef __cplusplus
diff --git a/upb/reflection.h b/upb/reflection.h
index 6071fba6f5..23a7d34c5d 100644
--- a/upb/reflection.h
+++ b/upb/reflection.h
@@ -32,9 +32,11 @@
 #include "upb/def.h"
 #include "upb/map.h"
 #include "upb/msg.h"
-#include "upb/port_def.inc"
 #include "upb/upb.h"
 
+// Must be last.
+#include "upb/port_def.inc"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/upb/status.h b/upb/status.h
index 2c5c2a7f8b..596691b30e 100644
--- a/upb/status.h
+++ b/upb/status.h
@@ -29,8 +29,8 @@
 #define UPB_STATUS_H_
 
 #include <stdarg.h>
-#include <stdbool.h>
 
+// Must be last.
 #include "upb/port_def.inc"
 
 #ifdef __cplusplus
@@ -57,10 +57,10 @@ void upb_Status_VSetErrorFormat(upb_Status* status, const char* fmt,
 void upb_Status_VAppendErrorFormat(upb_Status* status, const char* fmt,
                                    va_list args) UPB_PRINTF(2, 0);
 
-#include "upb/port_undef.inc"
-
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_STATUS_H_ */
diff --git a/upb/string_view.h b/upb/string_view.h
index 6a3395148e..95ebd4c1a8 100644
--- a/upb/string_view.h
+++ b/upb/string_view.h
@@ -64,10 +64,10 @@ UPB_INLINE bool upb_StringView_IsEqual(upb_StringView a, upb_StringView b) {
 #define UPB_STRINGVIEW_FORMAT "%.*s"
 #define UPB_STRINGVIEW_ARGS(view) (int)(view).size, (view).data
 
-#include "upb/port_undef.inc"
-
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_STRING_VIEW_H_ */
diff --git a/upb/text_encode.h b/upb/text_encode.h
index 2e817a3e50..312db24e35 100644
--- a/upb/text_encode.h
+++ b/upb/text_encode.h
@@ -30,6 +30,9 @@
 
 #include "upb/def.h"
 
+// Must be last.
+#include "upb/port_def.inc"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -61,4 +64,6 @@ size_t upb_TextEncode(const upb_Message* msg, const upb_MessageDef* m,
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_TEXTENCODE_H_ */
diff --git a/upb/upb.h b/upb/upb.h
index 20cb928f79..e77fd40bdb 100644
--- a/upb/upb.h
+++ b/upb/upb.h
@@ -152,10 +152,10 @@ UPB_INLINE int _upb_Log2Ceiling(int x) {
 
 UPB_INLINE int _upb_Log2CeilingSize(int x) { return 1 << _upb_Log2Ceiling(x); }
 
-#include "upb/port_undef.inc"
-
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
 
+#include "upb/port_undef.inc"
+
 #endif /* UPB_H_ */