diff --git a/src/mux/muxedit.c b/src/mux/muxedit.c
index 105db013..eac725ac 100644
--- a/src/mux/muxedit.c
+++ b/src/mux/muxedit.c
@@ -39,12 +39,6 @@ WebPMux* WebPNewInternal(int version) {
   }
 }
 
-static void DeleteAllChunks(WebPChunk** const chunk_list) {
-  while (*chunk_list) {
-    *chunk_list = ChunkDelete(*chunk_list);
-  }
-}
-
 // Delete all images in 'wpi_list'.
 static void DeleteAllImages(WebPMuxImage** const wpi_list) {
   while (*wpi_list != NULL) {
@@ -55,12 +49,12 @@ static void DeleteAllImages(WebPMuxImage** const wpi_list) {
 static void MuxRelease(WebPMux* const mux) {
   if (mux == NULL) return;
   DeleteAllImages(&mux->images_);
-  DeleteAllChunks(&mux->vp8x_);
-  DeleteAllChunks(&mux->iccp_);
-  DeleteAllChunks(&mux->anim_);
-  DeleteAllChunks(&mux->exif_);
-  DeleteAllChunks(&mux->xmp_);
-  DeleteAllChunks(&mux->unknown_);
+  ChunkListDelete(&mux->vp8x_);
+  ChunkListDelete(&mux->iccp_);
+  ChunkListDelete(&mux->anim_);
+  ChunkListDelete(&mux->exif_);
+  ChunkListDelete(&mux->xmp_);
+  ChunkListDelete(&mux->unknown_);
 }
 
 void WebPMuxDelete(WebPMux* mux) {
@@ -583,16 +577,6 @@ static WebPMuxError MuxCleanup(WebPMux* const mux) {
   return WEBP_MUX_OK;
 }
 
-// Total size of a list of chunks.
-static size_t ChunkListDiskSize(const WebPChunk* chunk_list) {
-  size_t size = 0;
-  while (chunk_list != NULL) {
-    size += ChunkDiskSize(chunk_list);
-    chunk_list = chunk_list->next_;
-  }
-  return size;
-}
-
 // Total size of a list of images.
 static size_t ImageListDiskSize(const WebPMuxImage* wpi_list) {
   size_t size = 0;
diff --git a/src/mux/muxi.h b/src/mux/muxi.h
index 20c12e8f..995e3f28 100644
--- a/src/mux/muxi.h
+++ b/src/mux/muxi.h
@@ -48,6 +48,7 @@ struct WebPMuxImage {
   WebPChunk*  header_;      // Corresponds to WEBP_CHUNK_ANMF/WEBP_CHUNK_FRGM.
   WebPChunk*  alpha_;       // Corresponds to WEBP_CHUNK_ALPHA.
   WebPChunk*  img_;         // Corresponds to WEBP_CHUNK_IMAGE.
+  WebPChunk*  unknown_;     // Corresponds to WEBP_CHUNK_UNKNOWN.
   int         width_;
   int         height_;
   int         has_alpha_;   // Through ALPH chunk or as part of VP8L.
@@ -136,6 +137,9 @@ WebPChunk* ChunkRelease(WebPChunk* const chunk);
 // Deletes given chunk & returns chunk->next_.
 WebPChunk* ChunkDelete(WebPChunk* const chunk);
 
+// Deletes all chunks in the given chunk list.
+void ChunkListDelete(WebPChunk** const chunk_list);
+
 // Returns size of the chunk including chunk header and padding byte (if any).
 static WEBP_INLINE size_t SizeWithPadding(size_t chunk_size) {
   return CHUNK_HEADER_SIZE + ((chunk_size + 1) & ~1U);
@@ -148,6 +152,9 @@ static WEBP_INLINE size_t ChunkDiskSize(const WebPChunk* chunk) {
   return SizeWithPadding(data_size);
 }
 
+// Total size of a list of chunks.
+size_t ChunkListDiskSize(const WebPChunk* chunk_list);
+
 // Write out the given list of chunks into 'dst'.
 uint8_t* ChunkListEmit(const WebPChunk* chunk_list, uint8_t* dst);
 
diff --git a/src/mux/muxinternal.c b/src/mux/muxinternal.c
index 56b2fcfe..0a620ec9 100644
--- a/src/mux/muxinternal.c
+++ b/src/mux/muxinternal.c
@@ -187,6 +187,12 @@ WebPChunk* ChunkDelete(WebPChunk* const chunk) {
   return next;
 }
 
+void ChunkListDelete(WebPChunk** const chunk_list) {
+  while (*chunk_list != NULL) {
+    *chunk_list = ChunkDelete(*chunk_list);
+  }
+}
+
 //------------------------------------------------------------------------------
 // Chunk serialization methods.
 
@@ -211,6 +217,15 @@ uint8_t* ChunkListEmit(const WebPChunk* chunk_list, uint8_t* dst) {
   return dst;
 }
 
+size_t ChunkListDiskSize(const WebPChunk* chunk_list) {
+  size_t size = 0;
+  while (chunk_list != NULL) {
+    size += ChunkDiskSize(chunk_list);
+    chunk_list = chunk_list->next_;
+  }
+  return size;
+}
+
 //------------------------------------------------------------------------------
 // Life of a MuxImage object.
 
@@ -225,6 +240,7 @@ WebPMuxImage* MuxImageRelease(WebPMuxImage* const wpi) {
   ChunkDelete(wpi->header_);
   ChunkDelete(wpi->alpha_);
   ChunkDelete(wpi->img_);
+  ChunkListDelete(&wpi->unknown_);
 
   next = wpi->next_;
   MuxImageInit(wpi);
@@ -356,6 +372,7 @@ size_t MuxImageDiskSize(const WebPMuxImage* const wpi) {
   if (wpi->header_ != NULL) size += ChunkDiskSize(wpi->header_);
   if (wpi->alpha_ != NULL) size += ChunkDiskSize(wpi->alpha_);
   if (wpi->img_ != NULL) size += ChunkDiskSize(wpi->img_);
+  if (wpi->unknown_ != NULL) size += ChunkListDiskSize(wpi->unknown_);
   return size;
 }
 
@@ -387,6 +404,7 @@ uint8_t* MuxImageEmit(const WebPMuxImage* const wpi, uint8_t* dst) {
   }
   if (wpi->alpha_ != NULL) dst = ChunkEmit(wpi->alpha_, dst);
   if (wpi->img_ != NULL) dst = ChunkEmit(wpi->img_, dst);
+  if (wpi->unknown_ != NULL) dst = ChunkListEmit(wpi->unknown_, dst);
   return dst;
 }
 
diff --git a/src/mux/muxread.c b/src/mux/muxread.c
index a30508e3..03259d9d 100644
--- a/src/mux/muxread.c
+++ b/src/mux/muxread.c
@@ -147,6 +147,11 @@ static int MuxImageParse(const WebPChunk* const chunk, int copy_data,
         if (!MuxImageFinalize(wpi)) goto Fail;
         wpi->is_partial_ = 0;  // wpi is completely filled.
         break;
+      case WEBP_CHUNK_UNKNOWN:
+        if (wpi->is_partial_) goto Fail;  // Encountered an unknown chunk
+                                          // before some image chunks.
+        if (ChunkSetNth(&subchunk, &wpi->unknown_, 0) != WEBP_MUX_OK) goto Fail;
+        break;
       default:
         goto Fail;
         break;