diff --git a/chrome/content/zotero/xpcom/collectionTreeView.js b/chrome/content/zotero/xpcom/collectionTreeView.js
index d8ebcc742..a0806f4c3 100644
--- a/chrome/content/zotero/xpcom/collectionTreeView.js
+++ b/chrome/content/zotero/xpcom/collectionTreeView.js
@@ -46,8 +46,9 @@ Zotero.CollectionTreeView = function()
  */
 Zotero.CollectionTreeView.prototype.setTree = function(treebox)
 {
-	if(this._treebox)
+	if (this._treebox || !treebox) {
 		return;
+	}
 	this._treebox = treebox;
 	
 	// Add a keypress listener for expand/collapse