diff --git a/libavcodec/h264.c b/libavcodec/h264.c
index d2b88d1d42..37b9d34814 100644
--- a/libavcodec/h264.c
+++ b/libavcodec/h264.c
@@ -3670,6 +3670,7 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
          h->height != h->avctx->coded_height  ||
          must_reinit ||
          needs_reinit)) {
+        h->context_initialized = 0;
         if (h != h0) {
             av_log(h->avctx, AV_LOG_ERROR,
                    "changing width %d -> %d / height %d -> %d on "