diff --git a/browser/components/customizableui/content/panelUI.js b/browser/components/customizableui/content/panelUI.js
index 11740856761e..c68c32e6ec9b 100644
--- a/browser/components/customizableui/content/panelUI.js
+++ b/browser/components/customizableui/content/panelUI.js
@@ -200,7 +200,7 @@ const PanelUI = {
     }
   },
 
-  isReady: function() {
+  get isReady() {
     return !!this._isReady;
   },
 
diff --git a/browser/components/customizableui/src/CustomizeMode.jsm b/browser/components/customizableui/src/CustomizeMode.jsm
index 9f91f192f1c0..e662782dac8a 100644
--- a/browser/components/customizableui/src/CustomizeMode.jsm
+++ b/browser/components/customizableui/src/CustomizeMode.jsm
@@ -191,7 +191,7 @@ CustomizeMode.prototype = {
       // is really not going to work. We pass "true" to ensureReady to
       // indicate that we're handling calling startBatchUpdate and
       // endBatchUpdate.
-      if (!window.PanelUI.isReady()) {
+      if (!window.PanelUI.isReady) {
         yield window.PanelUI.ensureReady(true);
       }