diff --git a/libavformat/avidec.c b/libavformat/avidec.c
index 5e9c1e3ed9..98d0267eea 100644
--- a/libavformat/avidec.c
+++ b/libavformat/avidec.c
@@ -1057,6 +1057,8 @@ static int read_gab2_sub(AVStream *st, AVPacket *pkt)
 
         ast->sub_ctx->pb = pb;
         if (!avformat_open_input(&ast->sub_ctx, "", sub_demuxer, NULL)) {
+            if (ast->sub_ctx->nb_streams != 1)
+                goto error;
             ff_read_packet(ast->sub_ctx, &ast->sub_pkt);
             *st->codec = *ast->sub_ctx->streams[0]->codec;
             ast->sub_ctx->streams[0]->codec->extradata = NULL;