diff --git a/src/components/controls.js b/src/components/controls.js
index c288c60..6a70f7d 100644
--- a/src/components/controls.js
+++ b/src/components/controls.js
@@ -48,7 +48,7 @@ export const ButtonIconControl = ({ attributes, setAttributes }) => {
 
   const { className } = attributes;
 
-  const classList = [...className.split( ' ' )];
+  const classList = className != undefined ? [...className.split( ' ' )] : '';
 
   const hasAlign = boolean => boolean ? 'right' : 'left';