diff --git a/libavformat/oggparsetheora.c b/libavformat/oggparsetheora.c
index e92d4c5170..6e6a362e1e 100644
--- a/libavformat/oggparsetheora.c
+++ b/libavformat/oggparsetheora.c
@@ -191,7 +191,7 @@ static int theora_packet(AVFormatContext *s, int idx)
         os->lastpts = os->lastdts   = theora_gptopts(s, idx, os->granule, NULL) - duration;
         if(s->streams[idx]->start_time == AV_NOPTS_VALUE) {
             s->streams[idx]->start_time = os->lastpts;
-            if (s->streams[idx]->duration)
+            if (s->streams[idx]->duration > 0)
                 s->streams[idx]->duration -= s->streams[idx]->start_time;
         }
     }