diff --git a/libavfilter/vsrc_sierpinski.c b/libavfilter/vsrc_sierpinski.c
index 898fb5ae54..72b28b1bd7 100644
--- a/libavfilter/vsrc_sierpinski.c
+++ b/libavfilter/vsrc_sierpinski.c
@@ -196,6 +196,7 @@ static int sierpinski_request_frame(AVFilterLink *link)
 
     frame->sample_aspect_ratio = (AVRational) {1, 1};
     frame->pts = s->pts++;
+    frame->duration = 1;
 
     draw_sierpinski(link->src, frame);