diff --git a/libavfilter/vsrc_mandelbrot.c b/libavfilter/vsrc_mandelbrot.c
index d4d7e2fa49..aa63f9edd1 100644
--- a/libavfilter/vsrc_mandelbrot.c
+++ b/libavfilter/vsrc_mandelbrot.c
@@ -395,6 +395,7 @@ static int request_frame(AVFilterLink *link)
 
     picref->sample_aspect_ratio = (AVRational) {1, 1};
     picref->pts = s->pts++;
+    picref->duration = 1;
 
     draw_mandelbrot(link->src, (uint32_t*)picref->data[0], picref->linesize[0]/4, picref->pts);
     return ff_filter_frame(link, picref);