diff --git a/build.js b/build.js
index 55a77c385..6e7a8b9ef 100755
--- a/build.js
+++ b/build.js
@@ -177,6 +177,7 @@
     'bottom',
     'firstArg',
     'hasDontEnumBug',
+    'hasEnumPrototype',
     'isKeysFast',
     'loop',
     'nonEnumArgs',
@@ -1924,8 +1925,9 @@
         // remove `prototype` [[Enumerable]] fix from `iteratorTemplate`
         source = source.replace(getIteratorTemplate(source), function(match) {
           return match
-            .replace(/(?: *\/\/.*\n)* *["'] *(?:<% *)?if *\(!hasDontEnumBug *(?:&&|\))[\s\S]+?<% *} *(?:%>|["']).+/g, '')
-            .replace(/!hasDontEnumBug *\|\|/g, '');
+            .replace(/(?: *\/\/.*\n)* *["']( *)<% *if *\(hasDontEnumBug[\s\S]+?["']\1<% *} *%>.+/, '')
+            .replace(/(?: *\/\/.*\n)* *["'] *(?:<% *)?if *\(hasEnumPrototype *(?:&&|\))[\s\S]+?<% *} *(?:%>|["']).+/g, '')
+            .replace(/hasEnumPrototype *\|\|/g, '');
         });
       }
       vm.runInContext(source, context);
@@ -2095,10 +2097,10 @@
           }
         });
 
-        // remove `hasDontEnumBug`, `iteratesOwnLast`, and `nonEnumArgs` declarations and assignments
+        // remove `hasDontEnumBug`, `hasEnumPrototype`, `iteratesOwnLast`, and `nonEnumArgs` declarations and assignments
         source = source
-          .replace(/^ *\(function\(\) *{[\s\S]+?}\(1\)\);\n/m, '')
-          .replace(/(?:\n +\/\*[^*]*\*+(?:[^\/][^*]*\*+)*\/)?\n *var (?:hasDontEnumBug|iteratesOwnLast|nonEnumArgs).+\n/g, '');
+          .replace(/(?:\n +\/\*[^*]*\*+(?:[^\/][^*]*\*+)*\/)?\n *var (?:hasDontEnumBug|hasEnumPrototype|iteratesOwnLast|nonEnumArgs).+\n/g, '')
+          .replace(/^ *\(function\(\) *{[\s\S]+?}\(1\)\);\n/m, '');
 
         // remove `iteratesOwnLast` from `shimIsPlainObject`
         source = source.replace(matchFunction(source, 'shimIsPlainObject'), function(match) {
@@ -2256,6 +2258,7 @@
       if ((source.match(/\bcreateIterator\b/g) || []).length < 2) {
         source = removeFunction(source, 'createIterator');
         source = source.replace(/(?:\n +\/\*[^*]*\*+(?:[^\/][^*]*\*+)*\/)?\n *var hasDontEnumBug;|.+?hasDontEnumBug *=.+/g, '');
+        source = source.replace(/(?:\n +\/\*[^*]*\*+(?:[^\/][^*]*\*+)*\/)?\n *var hasEnumPrototype;|.+?hasEnumPrototype *=.+/g, '');
         source = source.replace(/(?:\n +\/\*[^*]*\*+(?:[^\/][^*]*\*+)*\/)?\n *var nonEnumArgs;|.+?nonEnumArgs *=.+/g, '');
       }
       if (isRemoved(source, 'createIterator', 'bind', 'keys')) {
@@ -2267,8 +2270,8 @@
         source = removeVar(source, 'nativeKeys');
         source = removeKeysOptimization(source);
       }
-      if (!source.match(/var (?:hasDontEnumBug|iteratesOwnLast|nonEnumArgs)\b/g)) {
-        // remove `hasDontEnumBug`, `iteratesOwnLast`, and `nonEnumArgs` assignments
+      if (!source.match(/var (?:hasDontEnumBug|hasEnumPrototype|iteratesOwnLast|nonEnumArgs)\b/g)) {
+        // remove `hasDontEnumBug`, `hasEnumPrototype`, `iteratesOwnLast`, and `nonEnumArgs` assignments
         source = source.replace(/ *\(function\(\) *{[\s\S]+?}\(1\)\);\n/, '');
       }
     }
diff --git a/build/pre-compile.js b/build/pre-compile.js
index e727e3dfc..7b9dec296 100644
--- a/build/pre-compile.js
+++ b/build/pre-compile.js
@@ -40,6 +40,7 @@
     'bottom',
     'firstArg',
     'hasDontEnumBug',
+    'hasEnumPrototype',
     'isKeysFast',
     'loop',
     'nonEnumArgs',
diff --git a/lodash.js b/lodash.js
index 09599acd9..5c2e7b00f 100644
--- a/lodash.js
+++ b/lodash.js
@@ -127,6 +127,18 @@
    */
   var hasDontEnumBug;
 
+  /**
+   * Detect if a `prototype` properties are enumerable by default:
+   *
+   * Firefox < 3.6, Opera > 9.50 - Opera < 11.60, and Safari < 5.1
+   * (if the prototype or a property on the prototype has been set)
+   * incorrectly sets a function's `prototype` property [[Enumerable]]
+   * value to `true`. Because of this Lo-Dash standardizes on skipping
+   * the the `prototype` property of functions regardless of its
+   * [[Enumerable]] value.
+   */
+  var hasEnumPrototype;
+
   /** Detect if own properties are iterated after inherited properties (IE < 9) */
   var iteratesOwnLast;
 
@@ -154,6 +166,7 @@
     for (prop in arguments) { nonEnumArgs = !prop; }
 
     hasDontEnumBug = !/valueOf/.test(props);
+    hasEnumPrototype = propertyIsEnumerable.call(ctor, 'prototype');
     iteratesOwnLast = props[0] != 'x';
   }(1));
 
@@ -385,7 +398,7 @@
     // value to `true`. Because of this Lo-Dash standardizes on skipping
     // the the `prototype` property of functions regardless of its
     // [[Enumerable]] value.
-    '  <% if (!hasDontEnumBug) { %>\n' +
+    '  <% if (hasEnumPrototype) { %>\n' +
     "  var skipProto = typeof iterable == 'function' && \n" +
     "    propertyIsEnumerable.call(iterable, 'prototype');\n" +
     '  <% } %>' +
@@ -397,22 +410,22 @@
     '      length = ownProps.length;\n\n' +
     '  while (++ownIndex < length) {\n' +
     '    index = ownProps[ownIndex];\n' +
-    "    <% if (!hasDontEnumBug) { %>if (!(skipProto && index == 'prototype')) {\n  <% } %>" +
+    "    <% if (hasEnumPrototype) { %>if (!(skipProto && index == 'prototype')) {\n  <% } %>" +
     '    <%= loop %>\n' +
-    '    <% if (!hasDontEnumBug) { %>}\n<% } %>' +
+    '    <% if (hasEnumPrototype) { %>}\n<% } %>' +
     '  }' +
 
     // else using a for-in loop
     '  <% } else { %>\n' +
     '  for (index in iterable) {<%' +
-    '    if (!hasDontEnumBug || useHas) { %>\n    if (<%' +
-    "      if (!hasDontEnumBug) { %>!(skipProto && index == 'prototype')<% }" +
-    '      if (!hasDontEnumBug && useHas) { %> && <% }' +
+    '    if (hasEnumPrototype || useHas) { %>\n    if (<%' +
+    "      if (hasEnumPrototype) { %>!(skipProto && index == 'prototype')<% }" +
+    '      if (hasEnumPrototype && useHas) { %> && <% }' +
     '      if (useHas) { %>hasOwnProperty.call(iterable, index)<% }' +
     '    %>) {' +
     '    <% } %>\n' +
     '    <%= loop %>;' +
-    '    <% if (!hasDontEnumBug || useHas) { %>\n    }<% } %>\n' +
+    '    <% if (hasEnumPrototype || useHas) { %>\n    }<% } %>\n' +
     '  }' +
     '  <% } %>' +
 
@@ -678,6 +691,7 @@
     var data = {
       // support properties
       'hasDontEnumBug': hasDontEnumBug,
+      'hasEnumPrototype': hasEnumPrototype,
       'isKeysFast': isKeysFast,
       'nonEnumArgs': nonEnumArgs,
       'noCharByIndex': noCharByIndex,
@@ -931,7 +945,7 @@
    */
   var keys = !nativeKeys ? shimKeys : function(object) {
     // avoid iterating over the `prototype` property
-    return typeof object == 'function' && propertyIsEnumerable.call(object, 'prototype')
+    return hasEnumPrototype && typeof object == 'function' && propertyIsEnumerable.call(object, 'prototype')
       ? shimKeys(object)
       : (isObject(object) ? nativeKeys(object) : []);
   };