--- a/media/ffvpx/libavcodec/videodsp_template.c
+++ b/media/ffvpx/libavcodec/videodsp_template.c
@@ -43,8 +43,7 @@
         src += (h - 1) * src_linesize;
         src_y = h - 1;
     } else if (src_y <= -block_h) {
-        src -= src_y * src_linesize;
-        src += (1 - block_h) * src_linesize;
+        src += (-src_y + 1 - block_h) * src_linesize;
         src_y = 1 - block_h;
     }
     if (src_x >= w) {