diff --git a/zephyr/static/js/viewport.js b/zephyr/static/js/viewport.js
index 6a73b83e5d..62aa952cfe 100644
--- a/zephyr/static/js/viewport.js
+++ b/zephyr/static/js/viewport.js
@@ -2,8 +2,7 @@ var viewport = (function () {
 var exports = {};
 
 var jwindow;
-var height;
-var width;
+var dimensions = {};
 var in_stoppable_autoscroll = false;
 
 exports.at_top = function () {
@@ -94,28 +93,21 @@ exports.scrollTop = function viewport_scrollTop () {
     return jwindow.scrollTop.apply(jwindow, arguments);
 };
 
-exports.height = function viewport_height() {
-    if (arguments.length !== 0) {
-        height = undefined;
-        return jwindow.height.apply(jwindow, arguments);
-    }
-    if (height === undefined) {
-        height = $(window).height();
-    }
-    return height;
-};
-
-exports.width = function viewport_width() {
-    if (arguments.length !== 0) {
-        width = undefined;
-        return jwindow.width.apply(jwindow, arguments);
-    }
-    if (width === undefined) {
-        width = jwindow.width();
-    }
-    return width;
-};
+function make_dimen_wrapper(dimen_name, dimen_func) {
+    return function viewport_dimension_wrapper() {
+        if (arguments.length !== 0) {
+            delete dimensions[dimen_name];
+            return dimen_func.apply(jwindow, arguments);
+        }
+        if (! dimensions.hasOwnProperty(dimen_name)) {
+            dimensions[dimen_name] = dimen_func.call(jwindow);
+        }
+        return dimensions[dimen_name];
+    };
+}
 
+exports.height = make_dimen_wrapper('height', $(window).height);
+exports.width  = make_dimen_wrapper('width',  $(window).width);
 
 exports.stop_auto_scrolling = function() {
     if (in_stoppable_autoscroll) {
@@ -152,8 +144,7 @@ $(function () {
     jwindow = $(window);
     // This handler must be placed before all resize handlers in our application
     jwindow.resize(function () {
-        height = undefined;
-        width = undefined;
+        dimensions = {};
     });
 });