diff --git a/libavcodec/vp9.c b/libavcodec/vp9.c
index 745bbd6218..785b18725c 100644
--- a/libavcodec/vp9.c
+++ b/libavcodec/vp9.c
@@ -243,6 +243,8 @@ static int update_size(AVCodecContext *ctx, int w, int h)
     VP9Context *s = ctx->priv_data;
     uint8_t *p;
 
+    av_assert0(w > 0 && h > 0);
+
     if (s->above_partition_ctx && w == ctx->width && h == ctx->height)
         return 0;