--- a/testing/marionette/element.js
+++ b/testing/marionette/element.js
@@ -168,17 +168,17 @@ element.Store = class {
     if (!el) {
       throw new JavaScriptError(`Element reference not seen before: ${uuid}`);
     }
 
     try {
       el = el.get();
     } catch (e) {
       el = null;
-      delete this.els[id];
+      delete this.els[uuid];
     }
 
     // use XPCNativeWrapper to compare elements (see bug 834266)
     let wrappedFrame = new XPCNativeWrapper(container.frame);
     let wrappedShadowRoot;
     if (container.shadowRoot) {
       wrappedShadowRoot = new XPCNativeWrapper(container.shadowRoot);
     }