diff --git a/src/mux/muxedit.c b/src/mux/muxedit.c
index 0c4191e1..a486229c 100644
--- a/src/mux/muxedit.c
+++ b/src/mux/muxedit.c
@@ -306,6 +306,11 @@ WebPMuxError WebPMuxPushFrame(WebPMux* mux, const WebPMuxFrameInfo* frame,
   if (!(is_frame || (frame->id == WEBP_CHUNK_FRGM))) {
     return WEBP_MUX_INVALID_ARGUMENT;
   }
+#ifndef WEBP_EXPERIMENTAL_FEATURES
+  if (frame->id == WEBP_CHUNK_FRGM) {     // disabled for now.
+    return WEBP_MUX_INVALID_ARGUMENT;
+  }
+#endif
 
   if (bitstream->bytes == NULL || bitstream->size > MAX_CHUNK_PAYLOAD) {
     return WEBP_MUX_INVALID_ARGUMENT;
diff --git a/src/mux/muxread.c b/src/mux/muxread.c
index 8a3ff12f..0e074fb2 100644
--- a/src/mux/muxread.c
+++ b/src/mux/muxread.c
@@ -223,7 +223,9 @@ WebPMux* WebPMuxCreateInternal(const WebPData* bitstream, int copy_data,
         MuxImageInit(wpi);  // Reset for reading next image.
         break;
       case WEBP_CHUNK_ANMF:
+#ifdef WEBP_EXPERIMENTAL_FEATURES
       case WEBP_CHUNK_FRGM:
+#endif
         if (wpi->is_partial_) goto Err;  // Previous wpi is still incomplete.
         if (!MuxImageParse(&chunk, copy_data, wpi)) goto Err;
         ChunkRelease(&chunk);
@@ -378,6 +380,9 @@ static WebPMuxError MuxGetFrameFragmentInternal(const WebPMuxImage* const wpi,
   const int is_frame = (wpi->header_->tag_ == kChunks[IDX_ANMF].tag);
   const CHUNK_INDEX idx = is_frame ? IDX_ANMF : IDX_FRGM;
   const WebPData* frame_frgm_data;
+#ifndef WEBP_EXPERIMENTAL_FEATURES
+  if (!is_frame) return WEBP_MUX_INVALID_ARGUMENT;
+#endif
   assert(wpi->header_ != NULL);  // Already checked by WebPMuxGetFrame().
   // Get frame/fragment chunk.
   frame_frgm_data = &wpi->header_->data_;