diff --git a/frontend/app/utils/post-message.ts b/frontend/app/utils/post-message.ts
index a3f6a7eb..fb219299 100644
--- a/frontend/app/utils/post-message.ts
+++ b/frontend/app/utils/post-message.ts
@@ -56,7 +56,7 @@ export function postMessageToIframe(target: HTMLIFrameElement, data: ChildMessag
  */
 export function parseMessage({ data }: MessageEvent): AllMessages {
   if (typeof data !== 'object' || data === null || Array.isArray(data)) {
-    return {} as AllMessages;
+    return {};
   }
 
   return data as AllMessages;
diff --git a/frontend/templates/iframe.ejs b/frontend/templates/iframe.ejs
index e8a2b33f..8606c7c7 100644
--- a/frontend/templates/iframe.ejs
+++ b/frontend/templates/iframe.ejs
@@ -19,13 +19,16 @@
           return window.CSS && window.CSS.supports && window.CSS.supports('color', 'var(--fake-var)');
         }
         if (isCSSVariablesSupported()) {
-          var name;
           try {
-            name = JSON.parse(window.name);
-            if (name.__colors__) {
-              const colors = name.__colors__;
+            var name = JSON.parse(window.name);
+            var colors = name.__colors__;
+            var root = document.documentElement;
+            if (colors) {
               for (var color in colors) {
-                var root = document.documentElement;
+                if (!color.startsWith('--')) {
+                  console.info('Key ' + color + ' must start with `--`');
+                  continue;
+                }
                 root.style.setProperty(color, colors[color]);
               }
             }