diff --git a/src/dec/vp8l.c b/src/dec/vp8l.c
index 1f618e82..89b5b4bf 100644
--- a/src/dec/vp8l.c
+++ b/src/dec/vp8l.c
@@ -1142,11 +1142,12 @@ int VP8LDecodeAlphaImageStream(int width, int height, const uint8_t* const data,
   dec->action_ = READ_HDR;
   if (!DecodeImageStream(width, height, 1, dec, NULL)) goto Err;
 
-  // Special case: if alpha data contains only the color indexing transform
-  // (a frequent case), we will use DecodeAlphaData() method that only needs
-  // allocation of 1 byte per pixel (alpha channel).
+  // Special case: if alpha data uses only the color indexing transform and
+  // doesn't use color cache (a frequent case), we will use DecodeAlphaData()
+  // method that only needs allocation of 1 byte per pixel (alpha channel).
   if (dec->next_transform_ == 1 &&
-      dec->transforms_[0].type_ == COLOR_INDEXING_TRANSFORM) {
+      dec->transforms_[0].type_ == COLOR_INDEXING_TRANSFORM &&
+      dec->hdr_.color_cache_size_ == 0) {
     bytes_per_pixel = sizeof(uint8_t);
   }