diff --git a/backbone.js b/backbone.js
index ff7738f3..6bb95d9e 100644
--- a/backbone.js
+++ b/backbone.js
@@ -597,6 +597,7 @@
 
   // Mix in each Underscore method as a proxy to `Model#attributes`.
   _.each(modelMethods, function(method) {
+    if (!_[method]) return;
     Model.prototype[method] = function() {
       var args = slice.call(arguments);
       args.unshift(this.attributes);
@@ -978,6 +979,7 @@
 
   // Mix in each Underscore method as a proxy to `Collection#models`.
   _.each(methods, function(method) {
+    if (!_[method]) return;
     Collection.prototype[method] = function() {
       var args = slice.call(arguments);
       args.unshift(this.models);
@@ -990,6 +992,7 @@
 
   // Use attributes instead of properties.
   _.each(attributeMethods, function(method) {
+    if (!_[method]) return;
     Collection.prototype[method] = function(value, context) {
       var iterator = _.isFunction(value) ? value : function(model) {
         return model.get(value);