diff --git a/libavfilter/af_amerge.c b/libavfilter/af_amerge.c
index 8bcc0ac5be..801e592870 100644
--- a/libavfilter/af_amerge.c
+++ b/libavfilter/af_amerge.c
@@ -243,6 +243,10 @@ static int try_push_frame(AVFilterContext *ctx, int nb_samples)
     outbuf->pts = inbuf[0]->pts;
 
     outbuf->nb_samples     = nb_samples;
+    outbuf->duration = av_rescale_q(outbuf->nb_samples,
+                                    av_make_q(1, outlink->sample_rate),
+                                    outlink->time_base);
+
     if ((ret = av_channel_layout_copy(&outbuf->ch_layout, &outlink->ch_layout)) < 0)
         return ret;
 #if FF_API_OLD_CHANNEL_LAYOUT