diff --git a/src/addons/transitions/ReactTransitionGroup.js b/src/addons/transitions/ReactTransitionGroup.js
index 623838c49f..9e2d4911ab 100644
--- a/src/addons/transitions/ReactTransitionGroup.js
+++ b/src/addons/transitions/ReactTransitionGroup.js
@@ -44,6 +44,11 @@ var ReactTransitionGroupMixin = {
       'getTransitionConfig() method.'
     );
 
+    // don't animate undefined children
+    if (typeof sourceChildren === 'undefined') {
+      return;
+    }
+
     var children = {};
     var childMapping = ReactTransitionKeySet.getChildMapping(sourceChildren);
     var transitionConfig = this.getTransitionConfig();
diff --git a/src/addons/transitions/__tests__/ReactTransitionGroup-test.js b/src/addons/transitions/__tests__/ReactTransitionGroup-test.js
index bfddd7be5a..8455d3fba1 100644
--- a/src/addons/transitions/__tests__/ReactTransitionGroup-test.js
+++ b/src/addons/transitions/__tests__/ReactTransitionGroup-test.js
@@ -26,18 +26,18 @@ var mocks;
 // Most of the real functionality is covered in other unit tests, this just
 // makes sure we're wired up correctly.
 describe('ReactTransitionGroup', function() {
+  var container;
+
   beforeEach(function() {
     React = require('React');
     ReactTransitionGroup = require('ReactTransitionGroup');
     mocks = require('mocks');
+
+    container = document.createElement('div');
   });
 
   it('should warn after time with no transitionend', function() {
-    var container;
-    var a;
-
-    container = document.createElement('div');
-    a = React.renderComponent(
+    var a = React.renderComponent(
       <ReactTransitionGroup transitionName="yolo">
         <span key="one" id="one" />
       </ReactTransitionGroup>,
@@ -65,7 +65,6 @@ describe('ReactTransitionGroup', function() {
   });
 
   it('should keep both sets of DOM nodes around', function() {
-    var container = document.createElement('div');
     var a = React.renderComponent(
       <ReactTransitionGroup transitionName="yolo">
         <span key="one" id="one" />
@@ -83,4 +82,14 @@ describe('ReactTransitionGroup', function() {
     expect(a.getDOMNode().childNodes[0].id).toBe('two');
     expect(a.getDOMNode().childNodes[1].id).toBe('one');
   });
+
+  describe('with an undefined child', function () {
+    it('should fail silently', function () {
+      var a = React.renderComponent(
+        <ReactTransitionGroup transitionName="yolo">
+        </ReactTransitionGroup>,
+        container
+      );
+    });
+  });
 });