diff --git a/tools/ismindex.c b/tools/ismindex.c
index b801d43e8d..9efdebec28 100644
--- a/tools/ismindex.c
+++ b/tools/ismindex.c
@@ -251,7 +251,10 @@ static int get_video_private_data(struct VideoFile *vf, AVCodecContext *codec)
     if (codec->codec_id == AV_CODEC_ID_VC1)
         return get_private_data(vf, codec);
 
-    avio_open_dyn_buf(&io);
+    if (avio_open_dyn_buf(&io) < 0)  {
+        err = AVERROR(ENOMEM);
+        goto fail;
+    }
     if (codec->extradata_size < 11 || codec->extradata[0] != 1)
         goto fail;
     sps_size = AV_RB16(&codec->extradata[6]);