diff --git a/lib/map.js b/lib/map.js
index b5cbce7..7ece165 100644
--- a/lib/map.js
+++ b/lib/map.js
@@ -339,7 +339,7 @@ define(["map/clientlayer", "map/labelslayer",
           document.querySelector("head").innerHTML += "<link rel='stylesheet' class='css-mode' href='" + e.layer.options.mode + ".css'>";
           document.querySelector("html").classList.add(e.layer.options.mode);
           var cssInterval = setInterval(function () {
-            if (document.querySelector(".css-mode").sheet) {
+            if (typeof document.querySelector(".css-mode").sheet.cssRules != 'undefined') {
               labelsLayer.updateColor();
               clearInterval(cssInterval);
             }