diff --git a/src/core/ReactComponent.js b/src/core/ReactComponent.js
index 5c42a8e86f..bc3769df92 100644
--- a/src/core/ReactComponent.js
+++ b/src/core/ReactComponent.js
@@ -72,7 +72,7 @@ function isEmptyChild(child) {
 
 function assignKey(setKey, child, index) {
   if (ReactComponent.isValidComponent(child)) {
-    var key = child._key || child.props.key;
+    var key = child.props.key;
     if (__DEV__) {
       if (!HAS_WARNED && !key) {
         HAS_WARNED = true;
@@ -300,7 +300,7 @@ var ReactComponent = {
 
         } else if (!isEmptyChild(child)) {
 
-          if (ReactComponent.isValidComponent(child) && !child._key) {
+          if (ReactComponent.isValidComponent(child)) {
             // This is a static node and therefore safe to key by index.
             // No warning necessary.
             child._key = child.props.key || ('' + (i - 1));
diff --git a/src/core/__tests__/ReactIdentity-test.js b/src/core/__tests__/ReactIdentity-test.js
index ecf71a8553..e21be9d3bb 100644
--- a/src/core/__tests__/ReactIdentity-test.js
+++ b/src/core/__tests__/ReactIdentity-test.js
@@ -80,4 +80,75 @@ describe('ReactIdentity', function() {
       .toEqual('.reactRoot[0].:2.:chipmunk');
   });
 
+  it('should let restructured components retain their uniqueness', function() {
+    var instance0 = <span />;
+    var instance1 = <span />;
+    var instance2 = <span />;
+    var wrapped = <div>{instance0} {instance1}</div>;
+    var unwrappedAndAdded =
+      <div>
+        {instance2}
+        {wrapped.props.children[0]}
+        {wrapped.props.children[1]}
+      </div>;
+
+    expect(function() {
+
+      React.renderComponent(unwrappedAndAdded, document.createElement('div'));
+
+    }).not.toThrow();
+  });
+
+  it('should retain keys during updates in composite components', function() {
+
+    var TestComponent = React.createClass({
+      render: function() {
+        return <div>{this.props.children}</div>;
+      }
+    });
+
+    var TestContainer = React.createClass({
+
+      getInitialState: function() {
+        return { swapped: false };
+      },
+
+      swap: function() {
+        this.setState({ swapped: true });
+      },
+
+      render: function() {
+        return (
+          <TestComponent>
+            {this.state.swapped ? this.props.second : this.props.first}
+            {this.state.swapped ? this.props.first : this.props.second}
+          </TestComponent>
+        );
+      }
+
+    });
+
+    var instance0 = <span key="A" />;
+    var instance1 = <span key="B" />;
+
+    var wrapped = <TestContainer first={instance0} second={instance1} />;
+
+    React.renderComponent(wrapped, document.createElement('div'));
+
+    var beforeKey = wrapped
+      ._renderedComponent
+      ._renderedComponent
+      .props.children[0]._key;
+
+    wrapped.swap();
+
+    var afterKey = wrapped
+      ._renderedComponent
+      ._renderedComponent
+      .props.children[0]._key;
+
+    expect(beforeKey).not.toEqual(afterKey);
+
+  });
+
 });
diff --git a/src/utils/mapChildren.js b/src/utils/mapChildren.js
index cdba3e4d90..27079e8930 100644
--- a/src/utils/mapChildren.js
+++ b/src/utils/mapChildren.js
@@ -26,7 +26,7 @@ function mapChildren(children, mapFunction, context) {
     var child = children[ii];
     var key = child._key;
     var mappedChild = mapFunction.call(context, child, key, ii);
-    mappedChild._key = key;
+    mappedChild.props.key = key;
     mappedChildren.push(mappedChild);
   }
   return mappedChildren;