diff --git a/packages/mui-lab/src/TimelineConnector/TimelineConnector.js b/packages/mui-lab/src/TimelineConnector/TimelineConnector.js
index c0363f08e2f393..6fa85a3a63c3e6 100644
--- a/packages/mui-lab/src/TimelineConnector/TimelineConnector.js
+++ b/packages/mui-lab/src/TimelineConnector/TimelineConnector.js
@@ -22,7 +22,7 @@ const TimelineConnectorRoot = styled('span', {
 })(({ theme }) => {
   return {
     width: 2,
-    backgroundColor: theme.palette.grey[400],
+    backgroundColor: (theme.vars || theme).palette.grey[400],
     flexGrow: 1,
   };
 });