diff --git a/backbone.js b/backbone.js
index fd044cd7..03006acc 100644
--- a/backbone.js
+++ b/backbone.js
@@ -251,7 +251,7 @@
     this.attributes = {};
     if (options.collection) this.collection = options.collection;
     if (options.parse) attrs = this.parse(attrs, options) || {};
-    options._attrs = attrs;
+    options._attrs || (options._attrs = attrs);
     if (defaults = _.result(this, 'defaults')) {
       attrs = _.defaults({}, attrs, defaults);
     }
@@ -685,6 +685,7 @@
           if (remove) modelMap[existing.cid] = true;
           if (merge) {
             attrs = attrs === model ? model.attributes : options._attrs;
+            delete options._attrs;
             existing.set(attrs, options);
             if (sortable && !sort && existing.hasChanged(sortAttr)) sort = true;
           }
diff --git a/test/collection.js b/test/collection.js
index 915579fd..f35d67fe 100644
--- a/test/collection.js
+++ b/test/collection.js
@@ -967,6 +967,22 @@ $(document).ready(function() {
     equal(col.length, 1);
   });
 
+  test('merge without mutation', function () {
+    var Model = Backbone.Model.extend({
+      initialize: function (attrs, options) {
+        if (attrs.child) {
+          this.set('child', new Model(attrs.child, options), options);
+        }
+      }
+    });
+    var Collection = Backbone.Collection.extend({model: Model});
+    var data = [{id: 1, child: {id: 2}}];
+    var collection = new Collection(data);
+    equal(collection.first().id, 1);
+    collection.set(data);
+    equal(collection.first().id, 1);
+  });
+
   test("`set` and model level `parse`", function() {
     var Model = Backbone.Model.extend({
       parse: function (res) { return res.model; }