diff --git a/underscore.js b/underscore.js
index 9b366cb5f..88da6e1d8 100644
--- a/underscore.js
+++ b/underscore.js
@@ -371,9 +371,12 @@
   // been sorted, you have the option of using a faster algorithm.
   // Aliased as `unique`.
   _.uniq = _.unique = function(array, isSorted, iterator) {
+    var initial = iterator ? _.map(array, iterator) : array;
     var results = [];
-    _.reduce(iterator ? _.map(array, iterator) : array, function (memo, value, index) {
-      if (array.length < 3 || isSorted ? _.last(memo) !== value || !memo.length : !_.include(memo, value)) {
+    // The `isSorted` flag is irrelevant if the array only contains two elements.
+    if (array.length < 3) isSorted = true;
+    _.reduce(initial, function (memo, value, index) {
+      if (isSorted ? _.last(memo) !== value || !memo.length : !_.include(memo, value)) {
         memo.push(value);
         results.push(array[index]);
       }