diff --git a/php/ext/google/protobuf/php-upb.c b/php/ext/google/protobuf/php-upb.c
index facb63d11b82..f93d7facf545 100644
--- a/php/ext/google/protobuf/php-upb.c
+++ b/php/ext/google/protobuf/php-upb.c
@@ -4013,8 +4013,8 @@ void _upb_Message_DiscardUnknown_shallow(upb_Message* msg) {
   UPB_ASSERT(!upb_Message_IsFrozen(msg));
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   if (!in) return;
-  size_t size = 0;
-  for (size_t i = 0; i < in->size; i++) {
+  uint32_t size = 0;
+  for (uint32_t i = 0; i < in->size; i++) {
     upb_TaggedAuxPtr tagged_ptr = in->aux_data[i];
     if (upb_TaggedAuxPtr_IsExtension(tagged_ptr)) {
       in->aux_data[size++] = tagged_ptr;
@@ -4094,7 +4094,7 @@ void upb_Message_Freeze(upb_Message* msg, const upb_MiniTable* m) {
   // Extensions.
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   // TODO: b/376969853 - use iterator API
-  size_t size = in ? in->size : 0;
+  uint32_t size = in ? in->size : 0;
   for (size_t i = 0; i < size; i++) {
     upb_TaggedAuxPtr tagged_ptr = in->aux_data[i];
     if (!upb_TaggedAuxPtr_IsExtension(tagged_ptr)) {
@@ -12491,7 +12491,7 @@ const float kUpb_FltInfinity = UPB_INFINITY;
 const double kUpb_Infinity = UPB_INFINITY;
 const double kUpb_NaN = UPB_NAN;
 
-static size_t _upb_Message_SizeOfInternal(size_t count) {
+static size_t _upb_Message_SizeOfInternal(uint32_t count) {
   return UPB_SIZEOF_FLEX(upb_Message_Internal, aux_data, count);
 }
 
@@ -12501,7 +12501,7 @@ bool UPB_PRIVATE(_upb_Message_ReserveSlot)(struct upb_Message* msg,
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   if (!in) {
     // No internal data, allocate from scratch.
-    size_t capacity = 4;
+    uint32_t capacity = 4;
     in = upb_Arena_Malloc(a, _upb_Message_SizeOfInternal(capacity));
     if (!in) return false;
     in->size = 0;
@@ -12509,7 +12509,7 @@ bool UPB_PRIVATE(_upb_Message_ReserveSlot)(struct upb_Message* msg,
     UPB_PRIVATE(_upb_Message_SetInternal)(msg, in);
   } else if (in->capacity == in->size) {
     // Internal data is too small, reallocate.
-    size_t new_capacity = upb_RoundUpToPowerOfTwo(in->size + 1);
+    uint32_t new_capacity = upb_RoundUpToPowerOfTwo(in->size + 1);
     in = upb_Arena_Realloc(a, in, _upb_Message_SizeOfInternal(in->capacity),
                            _upb_Message_SizeOfInternal(new_capacity));
     if (!in) return false;
diff --git a/php/ext/google/protobuf/php-upb.h b/php/ext/google/protobuf/php-upb.h
index def0094443a7..209d1ddefc20 100644
--- a/php/ext/google/protobuf/php-upb.h
+++ b/php/ext/google/protobuf/php-upb.h
@@ -3097,8 +3097,8 @@ upb_TaggedAuxPtr_MakeUnknownData(const upb_StringView* sv) {
 
 typedef struct upb_Message_Internal {
   // Total number of entries set in aux_data
-  size_t size;
-  size_t capacity;
+  uint32_t size;
+  uint32_t capacity;
   // Tagged pointers to upb_StringView or upb_Extension
   upb_TaggedAuxPtr aux_data[];
 } upb_Message_Internal;
@@ -3210,7 +3210,7 @@ UPB_INLINE bool UPB_PRIVATE(_upb_Message_NextExtensionReverse)(
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   if (!in) return false;
   uintptr_t i = *iter;
-  size_t size = in->size;
+  uint32_t size = in->size;
   while (i < size) {
     upb_TaggedAuxPtr tagged_ptr = in->aux_data[size - 1 - i];
     i++;
diff --git a/ruby/ext/google/protobuf_c/ruby-upb.c b/ruby/ext/google/protobuf_c/ruby-upb.c
index 870216df1520..16ac51b2728e 100644
--- a/ruby/ext/google/protobuf_c/ruby-upb.c
+++ b/ruby/ext/google/protobuf_c/ruby-upb.c
@@ -4013,8 +4013,8 @@ void _upb_Message_DiscardUnknown_shallow(upb_Message* msg) {
   UPB_ASSERT(!upb_Message_IsFrozen(msg));
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   if (!in) return;
-  size_t size = 0;
-  for (size_t i = 0; i < in->size; i++) {
+  uint32_t size = 0;
+  for (uint32_t i = 0; i < in->size; i++) {
     upb_TaggedAuxPtr tagged_ptr = in->aux_data[i];
     if (upb_TaggedAuxPtr_IsExtension(tagged_ptr)) {
       in->aux_data[size++] = tagged_ptr;
@@ -4094,7 +4094,7 @@ void upb_Message_Freeze(upb_Message* msg, const upb_MiniTable* m) {
   // Extensions.
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   // TODO: b/376969853 - use iterator API
-  size_t size = in ? in->size : 0;
+  uint32_t size = in ? in->size : 0;
   for (size_t i = 0; i < size; i++) {
     upb_TaggedAuxPtr tagged_ptr = in->aux_data[i];
     if (!upb_TaggedAuxPtr_IsExtension(tagged_ptr)) {
@@ -11978,7 +11978,7 @@ const float kUpb_FltInfinity = UPB_INFINITY;
 const double kUpb_Infinity = UPB_INFINITY;
 const double kUpb_NaN = UPB_NAN;
 
-static size_t _upb_Message_SizeOfInternal(size_t count) {
+static size_t _upb_Message_SizeOfInternal(uint32_t count) {
   return UPB_SIZEOF_FLEX(upb_Message_Internal, aux_data, count);
 }
 
@@ -11988,7 +11988,7 @@ bool UPB_PRIVATE(_upb_Message_ReserveSlot)(struct upb_Message* msg,
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   if (!in) {
     // No internal data, allocate from scratch.
-    size_t capacity = 4;
+    uint32_t capacity = 4;
     in = upb_Arena_Malloc(a, _upb_Message_SizeOfInternal(capacity));
     if (!in) return false;
     in->size = 0;
@@ -11996,7 +11996,7 @@ bool UPB_PRIVATE(_upb_Message_ReserveSlot)(struct upb_Message* msg,
     UPB_PRIVATE(_upb_Message_SetInternal)(msg, in);
   } else if (in->capacity == in->size) {
     // Internal data is too small, reallocate.
-    size_t new_capacity = upb_RoundUpToPowerOfTwo(in->size + 1);
+    uint32_t new_capacity = upb_RoundUpToPowerOfTwo(in->size + 1);
     in = upb_Arena_Realloc(a, in, _upb_Message_SizeOfInternal(in->capacity),
                            _upb_Message_SizeOfInternal(new_capacity));
     if (!in) return false;
diff --git a/ruby/ext/google/protobuf_c/ruby-upb.h b/ruby/ext/google/protobuf_c/ruby-upb.h
index 057409fb9ac9..f106ae5bbdef 100755
--- a/ruby/ext/google/protobuf_c/ruby-upb.h
+++ b/ruby/ext/google/protobuf_c/ruby-upb.h
@@ -3099,8 +3099,8 @@ upb_TaggedAuxPtr_MakeUnknownData(const upb_StringView* sv) {
 
 typedef struct upb_Message_Internal {
   // Total number of entries set in aux_data
-  size_t size;
-  size_t capacity;
+  uint32_t size;
+  uint32_t capacity;
   // Tagged pointers to upb_StringView or upb_Extension
   upb_TaggedAuxPtr aux_data[];
 } upb_Message_Internal;
@@ -3212,7 +3212,7 @@ UPB_INLINE bool UPB_PRIVATE(_upb_Message_NextExtensionReverse)(
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   if (!in) return false;
   uintptr_t i = *iter;
-  size_t size = in->size;
+  uint32_t size = in->size;
   while (i < size) {
     upb_TaggedAuxPtr tagged_ptr = in->aux_data[size - 1 - i];
     i++;