diff --git a/src/panel.scss b/src/panel.scss
index 8a54338c20..6543465eed 100644
--- a/src/panel.scss
+++ b/src/panel.scss
@@ -60,7 +60,7 @@
 
 .panel-heading,
 .panel-footer {
-  --panel-heading-height-padding: calc(var(--panelHeaderSize) * 0.2);
+  --panel-heading-height-padding: calc(var(--panelHeaderSize, 3.2rem) * 0.2);
   --__panel-heading-gap: calc(var(--panelHeaderSize) * 0.1);
   --__panel-heading-height: var(--panelHeaderSize, 3.2em);
   --__panel-heading-height-inner: calc(var(--__panel-heading-height) - 2 * var(--panel-heading-height-padding, 0));