diff --git a/.eslintrc b/.eslintrc
index 2c46d63de..bc7da0540 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -20,7 +20,7 @@
     "no-floating-decimal": 2,
     "no-inner-declarations": 2,
     "no-lonely-if": 1,
-    "no-nested-ternary": 2,
+    "no-nested-ternary": 0,
     "no-new-object": 0,
     "no-new-func": 0,
     "no-underscore-dangle": 0,
diff --git a/test/arrays.js b/test/arrays.js
index 5706a6442..2799011f4 100644
--- a/test/arrays.js
+++ b/test/arrays.js
@@ -136,6 +136,17 @@
     equal(_.sortedIndex(array, 2147483648), 2147483648, 'should work with large indexes');
   });
 
+  test('sortedIndex conforms to sortBy (#1768)', function() {
+    var sorted = _([{a: NaN}, {a: NaN}, {a: void 0}, {a: 0}, {a: 1}, {a: 2}, {a: 3}, {a: '4'}, {a: 'foo'}])
+                  .sortBy('a');
+    _.each([0, 1, 2, 3, '4', 'foo'], function(val) {
+      equal(_.sortedIndex(sorted, {a: val}, 'a'), _.findIndex(sorted, {a: val}), 'For val: ' + val);
+    });
+
+    sorted = _.sortBy([undefined, 1, undefined, 2]);
+    equal(_.sortedIndex(sorted, undefined, _.identity), 2);
+  });
+
   test('uniq', function() {
     var list = [1, 2, 1, 3, 1, 4];
     deepEqual(_.uniq(list), [1, 2, 3, 4], 'can find the unique values of an unsorted array');
diff --git a/test/utility.js b/test/utility.js
index 0330f0dbe..fd5338844 100644
--- a/test/utility.js
+++ b/test/utility.js
@@ -78,6 +78,40 @@
     ok(diff <= 0 && diff > -5, 'Produces the correct time in milliseconds');//within 5ms
   });
 
+  test('comparator', function() {
+    _.each([
+      [2, 1],
+      [2, '1'],
+      ['2', 1],
+      [1.0001, 1],
+      [1, null],
+      [null, -1],
+      [void 0, null],
+      [void 0, 5],
+      [NaN, 'something'],
+      ['b', 'a'],
+      [-5, '-6.05']
+    ], function(vals) {
+      var a = vals[0], b = vals[1];
+      equal(_.comparator(a, b), 1, '\'' + a + '\' >= \'' + b + '\'');
+      equal(_.comparator(b, a), -1, '\'' + b + '\' <= \'' + a + '\'');
+    });
+
+    _.each([
+      [0, 0],
+      [null, 0],
+      [void 0, void 0],
+      [NaN, NaN],
+      [1, {valueOf: _.constant(1)}],
+      [1, '1'],
+      ['zap', 'zap']
+    ], function(vals) {
+      var a = vals[0], b = vals[1];
+      equal(_.comparator(a, b), 0, '\'' + a + '\' == \'' + b + '\'');
+      equal(_.comparator(b, a), 0, '\'' + b + '\' == \'' + a + '\'');
+    });
+  });
+
   test('uniqueId', function() {
     var ids = [], i = 0;
     while (i++ < 100) ids.push(_.uniqueId());
diff --git a/underscore.js b/underscore.js
index 8dc638003..c92146344 100644
--- a/underscore.js
+++ b/underscore.js
@@ -397,13 +397,7 @@
         criteria: iteratee(value, index, list)
       };
     }).sort(function(left, right) {
-      var a = left.criteria;
-      var b = right.criteria;
-      if (a !== b) {
-        if (a > b || a === void 0) return 1;
-        if (a < b || b === void 0) return -1;
-      }
-      return left.index - right.index;
+      return _.comparator(left.criteria, right.criteria) || left.index - right.index;
     }), 'value');
   };
 
@@ -675,7 +669,7 @@
     var low = 0, high = array.length;
     while (low < high) {
       var mid = Math.floor((low + high) / 2);
-      if (iteratee(array[mid]) < value) low = mid + 1; else high = mid;
+      if (_.comparator(iteratee(array[mid]), value) < 0) low = mid + 1; else high = mid;
     }
     return low;
   };
@@ -1299,6 +1293,18 @@
     };
   };
 
+  // Default internal comparator for determining whether a is greater (1),
+  // equal (0) or less than (-1) some object b
+  _.comparator = function(a, b) {
+    if (a === b) return 0;
+    var isAComparable = a >= a, isBComparable = b >= b;
+    if (isAComparable || isBComparable) {
+      if (isAComparable && !isBComparable) return -1;
+      if (isBComparable && !isAComparable) return 1;
+    }
+    return a > b ? 1 : (b > a) ? -1 : 0;
+  };
+
   // Run a function **n** times.
   _.times = function(n, iteratee, context) {
     var accum = Array(Math.max(0, n));