diff --git a/examples/libraries/toolBars.js b/examples/libraries/toolBars.js
index 16c68a73fb..abe8de8cc3 100644
--- a/examples/libraries/toolBars.js
+++ b/examples/libraries/toolBars.js
@@ -362,8 +362,11 @@ ToolBar = function(x, y, direction, optionalPersistenceKey, optionalInitialPosit
         this.fractionKey = optionalPersistenceKey + '.fraction';
         this.save = function () {
             var screenSize = Controller.getViewportDimensions();
-            var fraction = {x: that.x / screenSize.x, y: that.y / screenSize.y};
-            Settings.setValue(this.fractionKey, JSON.stringify(fraction));
+            if (screenSize.x > 0 && screenSize.y > 0) {
+                // Guard against invalid screen size that can occur at shut-down.
+                var fraction = {x: that.x / screenSize.x, y: that.y / screenSize.y};
+                Settings.setValue(this.fractionKey, JSON.stringify(fraction));
+            }
         }
     } else {
         this.save = function () { }; // Called on move. Can be overriden or extended by clients.