diff --git a/src/utils/ReactChildren.js b/src/utils/ReactChildren.js
index 4109557dde91e..e470609bc74c8 100644
--- a/src/utils/ReactChildren.js
+++ b/src/utils/ReactChildren.js
@@ -81,7 +81,7 @@ function mapSingleChildIntoContext(traverseContext, child, name, i) {
   var mapBookKeeping = traverseContext;
   var mapResult = mapBookKeeping.mapResult;
 
-  var keyUnique = !mapResult.hasOwnProperty(name);
+  var keyUnique = (mapResult[name] === undefined);
   if (__DEV__) {
     warning(
       keyUnique,
diff --git a/src/utils/flattenChildren.js b/src/utils/flattenChildren.js
index 5d8ee72b44561..3a5464d057012 100644
--- a/src/utils/flattenChildren.js
+++ b/src/utils/flattenChildren.js
@@ -22,7 +22,7 @@ var warning = require('warning');
 function flattenSingleChildIntoContext(traverseContext, child, name) {
   // We found a component instance.
   var result = traverseContext;
-  var keyUnique = !result.hasOwnProperty(name);
+  var keyUnique = (result[name] === undefined);
   if (__DEV__) {
     warning(
       keyUnique,