diff --git a/HISTORY.md b/HISTORY.md
index b101252..e205df7 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -8,6 +8,7 @@ https://github.com/josdejong/jsoneditor
 - Improved JSON schema titles on fields. Fixes #321. Thanks @AdamVig.
 - Added Simplified Chinese localization. Thanks @long2ice.
 - Added Turkish localization. Thanks @beratpostalci.
+- Fix #657: `onClassName` throwing an error when a node is removed.
 
 
 ## 2019-01-23, version 5.28.2
diff --git a/src/js/Node.js b/src/js/Node.js
index 00bd47b..b89eb78 100644
--- a/src/js/Node.js
+++ b/src/js/Node.js
@@ -932,7 +932,7 @@ Node.prototype._updateCssClassName = function () {
 
 Node.prototype.recursivelyUpdateCssClassesOnNodes = function () {  
   this._updateCssClassName();
-  if (this.childs !== 'undefined') {
+  if (Array.isArray(this.childs)) {
     for (var i = 0; i < this.childs.length; i++) {
       this.childs[i].recursivelyUpdateCssClassesOnNodes();
     }