diff --git a/lodash.src.js b/lodash.src.js
index 3d7add277..2634141b5 100644
--- a/lodash.src.js
+++ b/lodash.src.js
@@ -1606,18 +1606,20 @@
     }
 
     /**
-     * A specialized version of `_.sum` for arrays without support for iteratees.
+     * A specialized version of `_.sum` for arrays without support for callback
+     * shorthands and `this` binding..
      *
      * @private
      * @param {Array} array The array to iterate over.
+     * @param {Function} iteratee The function invoked per iteration.
      * @returns {number} Returns the sum.
      */
-    function arraySum(array) {
+    function arraySum(array, iteratee) {
       var length = array.length,
           result = 0;
 
       while (length--) {
-        result += +array[length] || 0;
+        result += +iteratee(array[length]) || 0;
       }
       return result;
     }
@@ -11948,15 +11950,9 @@
       if (thisArg && isIterateeCall(collection, iteratee, thisArg)) {
         iteratee = undefined;
       }
-      var callback = getCallback(),
-          noIteratee = iteratee == null;
-
-      if (!(noIteratee && callback === baseCallback)) {
-        noIteratee = false;
-        iteratee = callback(iteratee, thisArg, 3);
-      }
-      return noIteratee
-        ? arraySum(isArray(collection) ? collection : toIterable(collection))
+      iteratee = getCallback(iteratee, thisArg, 3);
+      return iteratee.length == 1
+        ? arraySum(isArray(collection) ? collection : toIterable(collection), iteratee)
         : baseSum(collection, iteratee);
     }