diff --git a/package.json b/package.json
index e466aeb..7d14049 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "mobx-rest",
-  "version": "0.0.10",
+  "version": "0.0.11",
   "description": "REST conventions for mobx.",
   "repository": {
     "type": "git",
diff --git a/src/Model.js b/src/Model.js
index 1eb84c6..0879cf3 100644
--- a/src/Model.js
+++ b/src/Model.js
@@ -30,8 +30,9 @@ class Model {
     attributes: {},
     {optimistic = true, patch = true}: SaveOptions = {}
   ): Promise<*> {
-    let data = Object.assign({}, attributes)
     let originalAttributes = this.attributes.toJS()
+    let newAttributes
+    let data
 
     if (!this.get('id')) {
       return this.collection.create(attributes, {optimistic})
@@ -40,9 +41,11 @@ class Model {
     const label: Label = 'updating'
 
     if (patch) {
-      data = Object.assign({}, originalAttributes, attributes)
+      newAttributes = Object.assign({}, originalAttributes, attributes)
+      data = Object.assign({}, attributes)
     } else {
-      data = attributes
+      newAttributes = Object.assign({}, attributes)
+      data = Object.assign({}, originalAttributes, attributes)
     }
 
     // TODO: use PATCH
@@ -51,7 +54,7 @@ class Model {
       data
     )
 
-    if (optimistic) this.attributes = asMap(data)
+    if (optimistic) this.attributes = asMap(newAttributes)
 
     this.request = {label, abort}