diff --git a/src/plots/cartesian/graph_interact.js b/src/plots/cartesian/graph_interact.js
index 9994260899c..ad122c5ba9e 100644
--- a/src/plots/cartesian/graph_interact.js
+++ b/src/plots/cartesian/graph_interact.js
@@ -2060,7 +2060,7 @@ function coverSlip() {
     cStyle.right = 0;
     cStyle.top = 0;
     cStyle.bottom = 0;
-    cStyle['z-index'] = 999999999;
+    cStyle.zIndex = 999999999;
     cStyle.background = 'none';
 
     document.body.appendChild(cover);