diff --git a/ruby/ext/google/protobuf_c/ruby-upb.h b/ruby/ext/google/protobuf_c/ruby-upb.h
index 00d96b4..512a822 100755
--- a/ruby/ext/google/protobuf_c/ruby-upb.h
+++ b/ruby/ext/google/protobuf_c/ruby-upb.h
@@ -3165,6 +3165,9 @@
   return ret;
 }
 
+// Sets the value of the given field in the given msg. The return value is true
+// if the operation completed successfully, or false if memory allocation
+// failed.
 UPB_INLINE bool upb_Message_SetField(upb_Message* msg,
                                      const upb_MiniTableField* field,
                                      upb_MessageValue val, upb_Arena* a) {