diff --git a/js/ui/environment.js b/js/ui/environment.js
index cb286d5bd..3144ec686 100644
--- a/js/ui/environment.js
+++ b/js/ui/environment.js
@@ -47,8 +47,11 @@ function _patchLayoutClass(layoutClass, styleProps) {
         layoutClass.prototype.hookup_style = function(container) {
             container.connect('style-changed', Lang.bind(this, function() {
                 let node = container.get_theme_node();
-                for (let prop in styleProps)
-                    this[prop] = node.get_length(styleProps[prop]);
+                for (let prop in styleProps) {
+                    let [found, length] = node.lookup_length(styleProps[prop], false);
+                    if (found)
+                        this[prop] = length;
+                }
             }));
         };
     layoutClass.prototype.child_set = function(actor, props) {