diff --git a/test/collections.js b/test/collections.js
index 1726629eb..857ae3731 100644
--- a/test/collections.js
+++ b/test/collections.js
@@ -1,4 +1,4 @@
-$(document).ready(function() {
+$(document).ready(function($, undefined) {
 
   module("Collections");
 
@@ -8,7 +8,7 @@ $(document).ready(function() {
     });
 
     var answers = [];
-    _.each([1, 2, 3], function(num){ answers.push(num * this.multiplier);}, {multiplier : 5});
+    _.each([1, 2, 3], function(num){ answers.push(num * this.multiplier); }, {multiplier : 5});
     equals(answers.join(', '), '5, 10, 15', 'context object property accessed');
 
     answers = [];
@@ -75,15 +75,14 @@ $(document).ready(function() {
       ifnull = ex;
     }
     ok(ifnull instanceof TypeError, 'handles a null (without inital value) properly');
-
     ok(_.reduce(null, function(){}, 138) === 138, 'handles a null (with initial value) properly');
+    equals(_.reduce([], function(){}, undefined), undefined, 'undefined can be passed as a special case');
+    raises(function() { _.reduce([], function(){}); }, TypeError, 'throws an error for empty arrays with no initial value');
 
-    // Sparse arrays:
-    var sparseArray  = [];
-    sparseArray[100] = 10;
-    sparseArray[200] = 20;
-
-    equals(_.reduce(sparseArray, function(a, b){ return a + b }), 30, 'initially-sparse arrays with no memo');
+    var sparseArray = [];
+    sparseArray[0] = 20;
+    sparseArray[2] = -5;
+    equals(_.reduce(sparseArray, function(a, b){ return a - b }), 25, 'initially-sparse arrays with no memo');
   });
 
   test('collections: reduceRight', function() {
@@ -103,8 +102,14 @@ $(document).ready(function() {
       ifnull = ex;
     }
     ok(ifnull instanceof TypeError, 'handles a null (without inital value) properly');
-
     ok(_.reduceRight(null, function(){}, 138) === 138, 'handles a null (with initial value) properly');
+    equals(_.reduceRight([], function(){}, undefined), undefined, 'undefined can be passed as a special case');
+    raises(function() { _.reduceRight([], function(){}); }, TypeError, 'throws an error for empty arrays with no initial value');
+
+    var sparseArray = [];
+    sparseArray[0] = 20;
+    sparseArray[2] = -5;
+    equals(_.reduceRight(sparseArray, function(a, b){ return a - b }), -25, 'initially-sparse arrays with no memo');
   });
 
   test('collections: detect', function() {
diff --git a/test/objects.js b/test/objects.js
index 6d432033a..fbcc02a39 100644
--- a/test/objects.js
+++ b/test/objects.js
@@ -1,18 +1,17 @@
-$(document).ready(function() {
+$(document).ready(function($, undefined) {
 
   module("Objects");
 
   test("objects: keys", function() {
-    var exception = /object/;
     equals(_.keys({one : 1, two : 2}).join(', '), 'one, two', 'can extract the keys from an object');
     // the test above is not safe because it relies on for-in enumeration order
     var a = []; a[1] = 0;
     equals(_.keys(a).join(', '), '1', 'is not fooled by sparse arrays; see issue #95');
-    raises(function() { _.keys(null); }, exception, 'throws an error for `null` values');
-    raises(function() { _.keys(void 0); }, exception, 'throws an error for `undefined` values');
-    raises(function() { _.keys(1); }, exception, 'throws an error for number primitives');
-    raises(function() { _.keys('a'); }, exception, 'throws an error for string primitives');
-    raises(function() { _.keys(true); }, exception, 'throws an error for boolean primitives');
+    raises(function() { _.keys(null); }, TypeError, 'throws an error for `null` values');
+    raises(function() { _.keys(void 0); }, TypeError, 'throws an error for `undefined` values');
+    raises(function() { _.keys(1); }, TypeError, 'throws an error for number primitives');
+    raises(function() { _.keys('a'); }, TypeError, 'throws an error for string primitives');
+    raises(function() { _.keys(true); }, TypeError, 'throws an error for boolean primitives');
   });
 
   test("objects: values", function() {
diff --git a/underscore.js b/underscore.js
index e535966b3..19f374db9 100644
--- a/underscore.js
+++ b/underscore.js
@@ -167,7 +167,7 @@
   // **Reduce** builds up a single result from a list of values, aka `inject`,
   // or `foldl`. Delegates to **ECMAScript 5**'s native `reduce` if available.
   _.reduce = _.foldl = _.inject = function(obj, iterator, memo, context) {
-    var initial = memo !== void 0;
+    var initial = arguments.length > 2;
     if (obj == null) obj = [];
     if (nativeReduce && obj.reduce === nativeReduce) {
       if (context) iterator = _.bind(iterator, context);
@@ -181,20 +181,22 @@
         memo = iterator.call(context, memo, value, index, list);
       }
     });
-    if (!initial) throw new TypeError("Reduce of empty array with no initial value");
+    if (!initial) throw new TypeError('Reduce of empty array with no initial value');
     return memo;
   };
 
   // The right-associative version of reduce, also known as `foldr`.
   // Delegates to **ECMAScript 5**'s native `reduceRight` if available.
   _.reduceRight = _.foldr = function(obj, iterator, memo, context) {
+    var initial = arguments.length > 2;
     if (obj == null) obj = [];
     if (nativeReduceRight && obj.reduceRight === nativeReduceRight) {
       if (context) iterator = _.bind(iterator, context);
-      return memo !== void 0 ? obj.reduceRight(iterator, memo) : obj.reduceRight(iterator);
+      return initial ? obj.reduceRight(iterator, memo) : obj.reduceRight(iterator);
     }
-    var reversed = (_.isArray(obj) ? obj.slice() : _.toArray(obj)).reverse();
-    return _.reduce(reversed, iterator, memo, context);
+    var reversed = _.toArray(obj).reverse();
+    if (context && !initial) iterator = _.bind(iterator, context);
+    return initial ? _.reduce(reversed, iterator, memo, context) : _.reduce(reversed, iterator);
   };
 
   // Return the first value which passes a truth test. Aliased as `detect`.