diff --git a/test/objects.js b/test/objects.js
index 48971c079..78add1fed 100644
--- a/test/objects.js
+++ b/test/objects.js
@@ -22,6 +22,10 @@ $(document).ready(function() {
   test("objects: functions", function() {
     var obj = {a : 'dash', b : _.map, c : (/yo/), d : _.reduce};
     ok(_.isEqual(['b', 'd'], _.functions(obj)), 'can grab the function names of any passed-in object');
+
+    var Animal = function(){};
+    Animal.prototype.run = function(){};
+    equals(_.functions(new Animal).join(''), 'run', 'also looks up functions on the prototype');
   });
 
   test("objects: extend", function() {
diff --git a/underscore.js b/underscore.js
index 5757609fa..9857159eb 100644
--- a/underscore.js
+++ b/underscore.js
@@ -559,7 +559,11 @@
   // Return a sorted list of the function names available on the object.
   // Aliased as `methods`
   _.functions = _.methods = function(obj) {
-    return _.filter(_.keys(obj), function(key){ return _.isFunction(obj[key]); }).sort();
+    var names = [];
+    for (var key in obj) {
+      if (_.isFunction(obj[key])) names.push(key);
+    }
+    return names.sort();
   };
 
   // Extend a given object with all the properties in passed-in object(s).