diff --git a/README.md b/README.md
index ce46145..5e9ee56 100644
--- a/README.md
+++ b/README.md
@@ -46,6 +46,15 @@ Input:  `{key1: val1, key2: val2}`
 
 Output: `{key1: key1, key2: key2}`
 
+You can specify the prefix for all values:
+
+```javascript
+keyMirror({
+  OPEN: null,
+  CLOSE: null
+}, 'WINDOW_');
+```
+
 I sometimes use this with lodash - use the following upon your first use of lodash to mix it in:
 
 ```javascript
diff --git a/index.js b/index.js
index 7f657b9..1195d6c 100644
--- a/index.js
+++ b/index.js
@@ -35,7 +35,8 @@
  * @param {object} obj
  * @return {object}
  */
-var keyMirror = function(obj) {
+var keyMirror = function(obj, prefix) {
+  prefix = prefix || '';
   var ret = {};
   var key;
   if (!(obj instanceof Object && !Array.isArray(obj))) {
@@ -43,7 +44,7 @@ var keyMirror = function(obj) {
   }
   for (key in obj) {
     if (obj.hasOwnProperty(key)) {
-      ret[key] = key;
+      ret[key] = prefix + key;
     }
   }
   return ret;