diff --git a/src/dom_components/model/ToolbarButton.js b/src/dom_components/model/ToolbarButton.js
index 74eaf7da1..c8703ee76 100644
--- a/src/dom_components/model/ToolbarButton.js
+++ b/src/dom_components/model/ToolbarButton.js
@@ -1,8 +1,10 @@
 import Backbone from 'backbone';
 
 export default class ToolbarButton extends Backbone.Model {
-  defaults = {
-    command: '',
-    attributes: {},
-  };
+  defaults() {
+    return {
+      command: '',
+      attributes: {},
+    };
+  }
 }