diff --git a/superset-frontend/src/dashboard/containers/DashboardPage.tsx b/superset-frontend/src/dashboard/containers/DashboardPage.tsx
index be0ba9177278c..80b937f8033fa 100644
--- a/superset-frontend/src/dashboard/containers/DashboardPage.tsx
+++ b/superset-frontend/src/dashboard/containers/DashboardPage.tsx
@@ -229,7 +229,7 @@ const DashboardPage: FC = () => {
   }, [dashboard_title]);
 
   useEffect(() => {
-    if (css) {
+    if (typeof css === 'string') {
       // returning will clean up custom css
       // when dashboard unmounts or changes
       return injectCustomCss(css);