diff --git a/sub/osd_libass.c b/sub/osd_libass.c
index 3a462e2717..1fbe6ddd00 100644
--- a/sub/osd_libass.c
+++ b/sub/osd_libass.c
@@ -256,7 +256,7 @@ static ASS_Style *prepare_osd_ass(struct osd_state *osd, struct osd_object *obj)
 
     double playresy = obj->ass.track->PlayResY;
     // Compensate for libass and mp_ass_set_style scaling the font etc.
-    if (!opts->osd_scale_by_window)
+    if (!opts->osd_scale_by_window && obj->vo_res.h)
         playresy *= 720.0 / obj->vo_res.h;
 
     ASS_Style *style = get_style(&obj->ass, "OSD");