diff --git a/src/view/tree.js b/src/view/tree.js
index bf45c46575..b6e1f99624 100644
--- a/src/view/tree.js
+++ b/src/view/tree.js
@@ -33,7 +33,7 @@
             el.parents('.panel').each(function(i, panel) {
                 panel = jQuery(panel);
                 var lengths = panel.css('box-shadow').match(/\d+px/g);
-                if (lengths.length) {
+                if (lengths && lengths.length) {
                     lengths = lengths.map(function(length) {
                         return length.replace('px', '');
                     });