diff --git a/php/ext/google/protobuf/php-upb.c b/php/ext/google/protobuf/php-upb.c
index b96d64f19b8d0..b40b76f7f298b 100644
--- a/php/ext/google/protobuf/php-upb.c
+++ b/php/ext/google/protobuf/php-upb.c
@@ -3921,7 +3921,7 @@ bool UPB_PRIVATE(_upb_Message_AddUnknown)(upb_Message* msg, const char* data,
   UPB_ASSERT(!upb_Message_IsFrozen(msg));
   // TODO: b/376969853  - Add debug check that the unknown field is an overall
   // valid proto field
-  if (!UPB_PRIVATE(_upb_Message_Realloc)(msg, len, arena)) return false;
+  if (!UPB_PRIVATE(_upb_Message_EnsureAvailable)(msg, len, arena)) return false;
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   memcpy(UPB_PTR_AT(in, in->unknown_end, char), data, len);
   in->unknown_end += len;
@@ -3938,7 +3938,8 @@ bool UPB_PRIVATE(_upb_Message_AddUnknownV)(struct upb_Message* msg,
   for (size_t i = 0; i < count; i++) {
     total_len += data[i].size;
   }
-  if (!UPB_PRIVATE(_upb_Message_Realloc)(msg, total_len, arena)) return false;
+  if (!UPB_PRIVATE(_upb_Message_EnsureAvailable)(msg, total_len, arena))
+    return false;
 
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   for (size_t i = 0; i < count; i++) {
@@ -12385,7 +12386,7 @@ upb_Extension* UPB_PRIVATE(_upb_Message_GetOrCreateExtension)(
   UPB_ASSERT(!upb_Message_IsFrozen(msg));
   upb_Extension* ext = (upb_Extension*)UPB_PRIVATE(_upb_Message_Getext)(msg, e);
   if (ext) return ext;
-  if (!UPB_PRIVATE(_upb_Message_Realloc)(msg, sizeof(upb_Extension), a))
+  if (!UPB_PRIVATE(_upb_Message_EnsureAvailable)(msg, sizeof(upb_Extension), a))
     return NULL;
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   in->ext_begin -= sizeof(upb_Extension);
@@ -12426,8 +12427,8 @@ const double kUpb_Infinity = INFINITY;
 
 const double kUpb_NaN = UPB_NAN;
 
-bool UPB_PRIVATE(_upb_Message_Realloc)(struct upb_Message* msg, size_t need,
-                                       upb_Arena* a) {
+bool UPB_PRIVATE(_upb_Message_EnsureAvailable)(struct upb_Message* msg,
+                                               size_t need, upb_Arena* a) {
   UPB_ASSERT(!upb_Message_IsFrozen(msg));
   const size_t overhead = sizeof(upb_Message_Internal);
 
diff --git a/php/ext/google/protobuf/php-upb.h b/php/ext/google/protobuf/php-upb.h
index aad02a6e30c0c..b0874336f1cd3 100644
--- a/php/ext/google/protobuf/php-upb.h
+++ b/php/ext/google/protobuf/php-upb.h
@@ -2608,8 +2608,11 @@ bool UPB_PRIVATE(_upb_Message_AddUnknownV)(struct upb_Message* msg,
                                            upb_Arena* arena,
                                            upb_StringView data[], size_t count);
 
-bool UPB_PRIVATE(_upb_Message_Realloc)(struct upb_Message* msg, size_t need,
-                                       upb_Arena* arena);
+// Ensure at least `need` unused bytes are available for unknown fields or
+// extensions. Returns false if a reallocation is needed to satisfy the request,
+// and fails.
+bool UPB_PRIVATE(_upb_Message_EnsureAvailable)(struct upb_Message* msg,
+                                               size_t need, upb_Arena* arena);
 
 #define kUpb_Message_UnknownBegin 0
 #define kUpb_Message_ExtensionBegin 0
diff --git a/ruby/ext/google/protobuf_c/ruby-upb.c b/ruby/ext/google/protobuf_c/ruby-upb.c
index 6bae049a73503..266b14e93800f 100644
--- a/ruby/ext/google/protobuf_c/ruby-upb.c
+++ b/ruby/ext/google/protobuf_c/ruby-upb.c
@@ -3921,7 +3921,7 @@ bool UPB_PRIVATE(_upb_Message_AddUnknown)(upb_Message* msg, const char* data,
   UPB_ASSERT(!upb_Message_IsFrozen(msg));
   // TODO: b/376969853  - Add debug check that the unknown field is an overall
   // valid proto field
-  if (!UPB_PRIVATE(_upb_Message_Realloc)(msg, len, arena)) return false;
+  if (!UPB_PRIVATE(_upb_Message_EnsureAvailable)(msg, len, arena)) return false;
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   memcpy(UPB_PTR_AT(in, in->unknown_end, char), data, len);
   in->unknown_end += len;
@@ -3938,7 +3938,8 @@ bool UPB_PRIVATE(_upb_Message_AddUnknownV)(struct upb_Message* msg,
   for (size_t i = 0; i < count; i++) {
     total_len += data[i].size;
   }
-  if (!UPB_PRIVATE(_upb_Message_Realloc)(msg, total_len, arena)) return false;
+  if (!UPB_PRIVATE(_upb_Message_EnsureAvailable)(msg, total_len, arena))
+    return false;
 
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   for (size_t i = 0; i < count; i++) {
@@ -11872,7 +11873,7 @@ upb_Extension* UPB_PRIVATE(_upb_Message_GetOrCreateExtension)(
   UPB_ASSERT(!upb_Message_IsFrozen(msg));
   upb_Extension* ext = (upb_Extension*)UPB_PRIVATE(_upb_Message_Getext)(msg, e);
   if (ext) return ext;
-  if (!UPB_PRIVATE(_upb_Message_Realloc)(msg, sizeof(upb_Extension), a))
+  if (!UPB_PRIVATE(_upb_Message_EnsureAvailable)(msg, sizeof(upb_Extension), a))
     return NULL;
   upb_Message_Internal* in = UPB_PRIVATE(_upb_Message_GetInternal)(msg);
   in->ext_begin -= sizeof(upb_Extension);
@@ -11913,8 +11914,8 @@ const double kUpb_Infinity = INFINITY;
 
 const double kUpb_NaN = UPB_NAN;
 
-bool UPB_PRIVATE(_upb_Message_Realloc)(struct upb_Message* msg, size_t need,
-                                       upb_Arena* a) {
+bool UPB_PRIVATE(_upb_Message_EnsureAvailable)(struct upb_Message* msg,
+                                               size_t need, upb_Arena* a) {
   UPB_ASSERT(!upb_Message_IsFrozen(msg));
   const size_t overhead = sizeof(upb_Message_Internal);
 
diff --git a/ruby/ext/google/protobuf_c/ruby-upb.h b/ruby/ext/google/protobuf_c/ruby-upb.h
index d0d4b25a6b50e..6593d47f7a2b0 100755
--- a/ruby/ext/google/protobuf_c/ruby-upb.h
+++ b/ruby/ext/google/protobuf_c/ruby-upb.h
@@ -2610,8 +2610,11 @@ bool UPB_PRIVATE(_upb_Message_AddUnknownV)(struct upb_Message* msg,
                                            upb_Arena* arena,
                                            upb_StringView data[], size_t count);
 
-bool UPB_PRIVATE(_upb_Message_Realloc)(struct upb_Message* msg, size_t need,
-                                       upb_Arena* arena);
+// Ensure at least `need` unused bytes are available for unknown fields or
+// extensions. Returns false if a reallocation is needed to satisfy the request,
+// and fails.
+bool UPB_PRIVATE(_upb_Message_EnsureAvailable)(struct upb_Message* msg,
+                                               size_t need, upb_Arena* arena);
 
 #define kUpb_Message_UnknownBegin 0
 #define kUpb_Message_ExtensionBegin 0