diff --git a/src/panel.scss b/src/panel.scss
index b36ad9b7..2f0b9ba5 100644
--- a/src/panel.scss
+++ b/src/panel.scss
@@ -59,7 +59,7 @@
   z-index: 2;
 
   &.-flexible-height {
-    --panel-heading-height: auto;
+    --__panel-heading-height: auto;
 
     &::after,
     &::before {