diff --git a/src/isomorphic/classic/element/ReactElementValidator.js b/src/isomorphic/classic/element/ReactElementValidator.js
index 41646c65bd..731d72a708 100644
--- a/src/isomorphic/classic/element/ReactElementValidator.js
+++ b/src/isomorphic/classic/element/ReactElementValidator.js
@@ -135,6 +135,9 @@ function getAddendaForKeyUse(messageType, element, parentType) {
  * @param {*} parentType node's parent's type.
  */
 function validateChildKeys(node, parentType) {
+  if (typeof node !== 'object') {
+    return;
+  }
   if (Array.isArray(node)) {
     for (var i = 0; i < node.length; i++) {
       var child = node[i];
diff --git a/src/isomorphic/classic/element/__tests__/ReactElementValidator-test.js b/src/isomorphic/classic/element/__tests__/ReactElementValidator-test.js
index 4bcb4085fc..c528fbb061 100644
--- a/src/isomorphic/classic/element/__tests__/ReactElementValidator-test.js
+++ b/src/isomorphic/classic/element/__tests__/ReactElementValidator-test.js
@@ -449,4 +449,24 @@ describe('ReactElementValidator', function() {
     expect(console.error.argsForCall.length).toBe(0);
   });
 
+  it('should not enumerate enumerable numbers (#4776)', function() {
+    /*eslint-disable no-extend-native */
+    Number.prototype['@@iterator'] = function() {
+      throw new Error('number iterator called');
+    };
+    /*eslint-enable no-extend-native */
+
+    try {
+      void (
+        <div>
+          {5}
+          {12}
+          {13}
+        </div>
+      );
+    } finally {
+      delete Number.prototype['@@iterator'];
+    }
+  });
+
 });
diff --git a/src/shared/utils/__tests__/traverseAllChildren-test.js b/src/shared/utils/__tests__/traverseAllChildren-test.js
index 013ee52f8d..5c95ec8828 100644
--- a/src/shared/utils/__tests__/traverseAllChildren-test.js
+++ b/src/shared/utils/__tests__/traverseAllChildren-test.js
@@ -435,4 +435,45 @@ describe('traverseAllChildren', function() {
     );
   });
 
+  it('should not enumerate enumerable numbers (#4776)', function() {
+    /*eslint-disable no-extend-native */
+    Number.prototype['@@iterator'] = function() {
+      throw new Error('number iterator called');
+    };
+    /*eslint-enable no-extend-native */
+
+    try {
+      var instance = (
+        <div>
+          {5}
+          {12}
+          {13}
+        </div>
+      );
+
+      var traverseFn = jasmine.createSpy();
+
+      traverseAllChildren(instance.props.children, traverseFn, null);
+      expect(traverseFn.calls.length).toBe(3);
+
+      expect(traverseFn).toHaveBeenCalledWith(
+        null,
+        5,
+        '.0'
+      );
+      expect(traverseFn).toHaveBeenCalledWith(
+        null,
+        12,
+        '.1'
+      );
+      expect(traverseFn).toHaveBeenCalledWith(
+        null,
+        13,
+        '.2'
+      );
+    } finally {
+      delete Number.prototype['@@iterator'];
+    }
+  });
+
 });