diff --git a/libavfilter/vf_zscale.c b/libavfilter/vf_zscale.c
index bb457423b3..bab87b0c94 100644
--- a/libavfilter/vf_zscale.c
+++ b/libavfilter/vf_zscale.c
@@ -799,7 +799,7 @@ static int filter_frame(AVFilterLink *link, AVFrame *in)
         link->dst->inputs[0]->w      = in->width;
         link->dst->inputs[0]->h      = in->height;
 
-        s->nb_threads = FFMIN(ff_filter_get_nb_threads(ctx), link->h / 8);
+        s->nb_threads = av_clip(FFMIN(ff_filter_get_nb_threads(ctx), FFMIN(link->h, outlink->h) / 8), 1, MAX_THREADS);
         s->in_colorspace = in->colorspace;
         s->in_trc = in->color_trc;
         s->in_primaries = in->color_primaries;