diff --git a/sub/osd_libass.c b/sub/osd_libass.c
index 667431eb7b..917bf2649c 100644
--- a/sub/osd_libass.c
+++ b/sub/osd_libass.c
@@ -367,6 +367,14 @@ static void get_osd_bar_box(struct osd_state *osd, struct osd_object *obj,
 
     mp_ass_set_style(style, track->PlayResY, opts->osd_style);
 
+    if (osd->opts->osd_style->back_color.a) {
+        // override the default osd opaque-box into plain outline. Otherwise
+        // the opaque box is not aligned with the bar (even without shadow),
+        // and each bar ass event gets its own opaque box - breaking the bar.
+        style->BackColour = MP_ASS_COLOR(opts->osd_style->shadow_color);
+        style->BorderStyle = 1; // outline
+    }
+
     *o_w = track->PlayResX * (opts->osd_bar_w / 100.0);
     *o_h = track->PlayResY * (opts->osd_bar_h / 100.0);