diff --git a/lib/resources/collection/index.js b/lib/resources/collection/index.js
index 3887009..8555b26 100644
--- a/lib/resources/collection/index.js
+++ b/lib/resources/collection/index.js
@@ -467,9 +467,13 @@ Collection.prototype.save = function (ctx, fn) {
       } 
       if(err) return done(err);
 
+      // copy previous obj
+      Object.keys(obj).forEach(function (key) {
+        prev[key] = obj[key];
+      });
+
       // merge changes
       Object.keys(item).forEach(function (key) {
-        prev[key] = obj[key];
         obj[key] = item[key];
       });