diff --git a/upb/test/fuzz_util.cc b/upb/test/fuzz_util.cc
index 685fd0f166d14..8b5aeb6b7a6cc 100644
--- a/upb/test/fuzz_util.cc
+++ b/upb/test/fuzz_util.cc
@@ -130,7 +130,9 @@ void Builder::BuildExtensions(upb_ExtensionRegistry** exts) {
                                         status.ptr());
       if (!ptr) break;
       if (!LinkExtension(ext)) continue;
-      if (upb_ExtensionRegistry_Lookup(*exts, ext->UPB_PRIVATE(extendee),
+      if (upb_MiniTable_FindFieldByNumber(ext->UPB_PRIVATE(extendee),
+                                          upb_MiniTableExtension_Number(ext)) ||
+          upb_ExtensionRegistry_Lookup(*exts, ext->UPB_PRIVATE(extendee),
                                        upb_MiniTableExtension_Number(ext)))
         continue;
       upb_ExtensionRegistry_AddArray(
diff --git a/upb/wire/decode_fast/field_unknown.c b/upb/wire/decode_fast/field_unknown.c
index e4c54163d5fd4..a902c930e2a32 100644
--- a/upb/wire/decode_fast/field_unknown.c
+++ b/upb/wire/decode_fast/field_unknown.c
@@ -57,6 +57,8 @@ UPB_FORCEINLINE bool _upb_FastDecoder_DoDecodeUnknown(
     // message is marked by an EndGroup tag. Since EndGroup tags are not in
     // the MiniTable, they are routed to the unknown field handler. We must
     // intercept them here to properly terminate the message.
+    _upb_Decoder_Trace(d, '<');
+    *ptr = start;
     return UPB_DECODEFAST_EXIT(kUpb_DecodeFastNext_FallbackToMiniTable, ret);
   }
 
@@ -110,6 +112,7 @@ UPB_FORCEINLINE bool _upb_FastDecoder_DoDecodeUnknown(
     return UPB_DECODEFAST_ERROR(d, kUpb_DecodeStatus_OutOfMemory, ret);
   }
 
+  _upb_Decoder_Trace(d, 'F');
   data = 0;
   return true;
 }