diff --git a/av1/common/blockd.h b/av1/common/blockd.h
index 00f2f1d..9b5bad2 100644
--- a/av1/common/blockd.h
+++ b/av1/common/blockd.h
@@ -799,7 +799,7 @@
 static INLINE BLOCK_SIZE get_plane_block_size(BLOCK_SIZE bsize,
                                               int subsampling_x,
                                               int subsampling_y) {
-  if (bsize == BLOCK_INVALID) return BLOCK_INVALID;
+  assert(bsize < BLOCK_SIZES_ALL);
   assert(subsampling_x >= 0 && subsampling_x < 2);
   assert(subsampling_y >= 0 && subsampling_y < 2);
   return ss_size_lookup[bsize][subsampling_x][subsampling_y];