diff --git a/libavfilter/src_avsynctest.c b/libavfilter/src_avsynctest.c
index c78e517ac3..78e4a2ba50 100644
--- a/libavfilter/src_avsynctest.c
+++ b/libavfilter/src_avsynctest.c
@@ -348,6 +348,7 @@ static int video_frame(AVFilterLink *outlink)
     }
 
     out->pts = s->vpts++;
+    out->duration = 1;
 
     return ff_filter_frame(outlink, out);
 }