diff --git a/lib/datastore.js b/lib/datastore.js
index e2350f4..69165fd 100644
--- a/lib/datastore.js
+++ b/lib/datastore.js
@@ -589,4 +589,6 @@ Datastore.prototype.remove = function () {
 
 
 
+
+
 module.exports = Datastore;
diff --git a/lib/model.js b/lib/model.js
index 7bca16b..709cf06 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -249,11 +249,18 @@ lastStepModifierFunctions.$push = function (obj, field, value) {
  * Note that it doesn't check whether the original array contains duplicates
  */
 lastStepModifierFunctions.$addToSet = function (obj, field, value) {
+  var addToSet = true;
+
   // Create the array if it doesn't exist
   if (!obj.hasOwnProperty(field)) { obj[field] = []; }
 
   if (!util.isArray(obj[field])) { throw "Can't $addToSet an element on non-array values"; }
-  if (obj[field].indexOf(value) === -1) { obj[field].push(value); }
+
+  obj[field].forEach(function (v) {
+    if (compareThings(v, value) === 0) { addToSet = false; }
+  });
+
+  if (addToSet) { obj[field].push(value); }
 };
 
 
diff --git a/test/model.test.js b/test/model.test.js
index 167a0ed..e1ef87a 100644
--- a/test/model.test.js
+++ b/test/model.test.js
@@ -410,6 +410,18 @@ describe('Model', function () {
         }).should.throw();
       });
 
+      it('Use deep-equality to check whether we can add a value to a set', function () {
+        var obj = { arr: [ { b: 2 } ] }
+          , modified;
+
+        modified = model.modify(obj, { $addToSet: { arr: { b: 3 } } });
+        assert.deepEqual(modified, { arr: [{ b: 2 }, { b: 3 }] });
+
+        obj = { arr: [ { b: 2 } ] }
+        modified = model.modify(obj, { $addToSet: { arr: { b: 2 } } });
+        assert.deepEqual(modified, { arr: [{ b: 2 }] });
+      });
+
     });   // End of '$addToSet modifier'
 
     describe('$pop modifier', function () {