diff --git a/av1/common/blockd.c b/av1/common/blockd.c
index 0aa0c30..2e796b6 100644
--- a/av1/common/blockd.c
+++ b/av1/common/blockd.c
@@ -99,6 +99,10 @@
     xd->plane[i].subsampling_x = i ? ss_x : 0;
     xd->plane[i].subsampling_y = i ? ss_y : 0;
   }
+  for (i = num_planes; i < MAX_MB_PLANE; i++) {
+    xd->plane[i].subsampling_x = 1;
+    xd->plane[i].subsampling_y = 1;
+  }
 }
 
 const int16_t dr_intra_derivative[90] = {