diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index 78bc6e7626..91c5e43c2e 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -557,6 +557,11 @@ int avcodec_default_reget_buffer(AVCodecContext *s, AVFrame *pic){
 
     assert(s->codec_type == AVMEDIA_TYPE_VIDEO);
 
+    if (pic->data[0] && (pic->width != s->width || pic->height != s->height || pic->format != s->pix_fmt)) {
+        av_log(s, AV_LOG_WARNING, "Width/height/fmt changing with reget buffer");
+        s->release_buffer(s, pic);
+    }
+
     /* If no picture return a new buffer */
     if(pic->data[0] == NULL) {
         /* We will copy from buffer, so must be readable */