diff --git a/libavfilter/af_channelmap.c b/libavfilter/af_channelmap.c
index cc66f0436f..f8289ccf5e 100644
--- a/libavfilter/af_channelmap.c
+++ b/libavfilter/af_channelmap.c
@@ -348,6 +348,7 @@ static int channelmap_filter_frame(AVFilterLink *inlink, AVFrame *buf)
            FFMIN(FF_ARRAY_ELEMS(buf->data), nch_out) * sizeof(buf->data[0]));
 
     buf->channel_layout = outlink->channel_layout;
+    av_frame_set_channels(buf, outlink->channels);
 
     return ff_filter_frame(outlink, buf);
 }