diff --git a/staging/src/k8s.io/client-go/tools/cache/shared_informer.go b/staging/src/k8s.io/client-go/tools/cache/shared_informer.go
index e91fc9e955..859099d077 100644
--- a/staging/src/k8s.io/client-go/tools/cache/shared_informer.go
+++ b/staging/src/k8s.io/client-go/tools/cache/shared_informer.go
@@ -260,7 +260,8 @@ func (s *sharedIndexInformer) AddIndexers(indexers Indexers) error {
 	defer s.startedLock.Unlock()
 
 	if s.started {
-		return fmt.Errorf("informer has already started")
+		s.blockDeltas.Lock()
+		defer s.blockDeltas.Unlock()
 	}
 
 	return s.indexer.AddIndexers(indexers)
diff --git a/staging/src/k8s.io/client-go/tools/cache/thread_safe_store.go b/staging/src/k8s.io/client-go/tools/cache/thread_safe_store.go
index 1c201efb62..a9512b4825 100644
--- a/staging/src/k8s.io/client-go/tools/cache/thread_safe_store.go
+++ b/staging/src/k8s.io/client-go/tools/cache/thread_safe_store.go
@@ -125,6 +125,11 @@ func (c *threadSafeMap) Replace(items map[string]interface{}, resourceVersion st
 	c.items = items
 
 	// rebuild any index
+	c.rebuildIndices()
+}
+
+// rebuildIndices rebuilds all indices for the current set c.items. Assumes that c.lock is held by caller
+func (c *threadSafeMap) rebuildIndices() {
 	c.indices = Indices{}
 	for key, item := range c.items {
 		c.updateIndices(nil, item, key)
@@ -222,10 +227,6 @@ func (c *threadSafeMap) AddIndexers(newIndexers Indexers) error {
 	c.lock.Lock()
 	defer c.lock.Unlock()
 
-	if len(c.items) > 0 {
-		return fmt.Errorf("cannot add indexers to running index")
-	}
-
 	oldKeys := sets.StringKeySet(c.indexers)
 	newKeys := sets.StringKeySet(newIndexers)
 
@@ -236,6 +237,11 @@ func (c *threadSafeMap) AddIndexers(newIndexers Indexers) error {
 	for k, v := range newIndexers {
 		c.indexers[k] = v
 	}
+
+	if len(c.items) > 0 {
+		c.rebuildIndices()
+	}
+
 	return nil
 }
 
diff --git a/staging/src/k8s.io/client-go/tools/cache/thread_safe_store_test.go b/staging/src/k8s.io/client-go/tools/cache/thread_safe_store_test.go
new file mode 100644
index 0000000000..35f7dd6f78
--- /dev/null
+++ b/staging/src/k8s.io/client-go/tools/cache/thread_safe_store_test.go
@@ -0,0 +1,115 @@
+/*
+Copyright 2014 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cache
+
+import (
+	"k8s.io/kubernetes/staging/src/k8s.io/apimachinery/pkg/util/sets"
+	"testing"
+)
+
+func TestAddIndexerAfterAdd(t *testing.T) {
+	store := NewThreadSafeStore(Indexers{}, Indices{})
+
+	// Add first indexer
+	err := store.AddIndexers(Indexers{
+		"first": func(obj interface{}) ([]string, error) {
+			value := obj.(string)
+			return []string{
+				value,
+			}, nil
+		},
+	})
+	if err != nil {
+		t.Errorf("failed to add first indexer")
+	}
+
+	// Add some data to index
+	store.Add("keya", "value")
+	store.Add("keyb", "value")
+
+	// Assert
+	indexKeys, _ := store.IndexKeys("first", "value")
+	expected := sets.NewString("keya", "keyb")
+	actual := sets.NewString(indexKeys...)
+	if !actual.Equal(expected) {
+		t.Errorf("expected %v does not match actual %v", expected, actual)
+	}
+
+	// Add same indexer, which should fail
+	err = store.AddIndexers(Indexers{
+		"first": func(interface{}) ([]string, error) {
+			return nil, nil
+		},
+	})
+	if err == nil {
+		t.Errorf("Add same index should have failed")
+	}
+
+	// Add new indexer
+	err = store.AddIndexers(Indexers{
+		"second": func(obj interface{}) ([]string, error) {
+			v := obj.(string)
+			return []string{
+				v +"2",
+			}, nil
+		},
+	})
+	if err != nil {
+		t.Errorf("failed to add second indexer")
+	}
+
+	// Assert indexers was added
+	if _, ok := store.GetIndexers()["first"]; !ok {
+		t.Errorf("missing indexer first")
+	}
+	if _, ok := store.GetIndexers()["second"]; !ok {
+		t.Errorf("missing indexer second")
+	}
+
+	// Assert existing data is re-indexed
+	indexKeys, _ = store.IndexKeys("first", "value")
+	expected = sets.NewString("keya", "keyb")
+	actual = sets.NewString(indexKeys...)
+	if !actual.Equal(expected) {
+		t.Errorf("expected %v does not match actual %v", expected, actual)
+	}
+	indexKeys, _ = store.IndexKeys("second", "value2")
+	expected = sets.NewString("keya", "keyb")
+	actual = sets.NewString(indexKeys...)
+	if !actual.Equal(expected) {
+		t.Errorf("expected %v does not match actual %v", expected, actual)
+	}
+
+	// Add more data
+	store.Add("keyc", "value")
+	store.Add("keyd", "value")
+
+	// Assert new data is indexed
+	indexKeys, _ = store.IndexKeys("first", "value")
+	expected = sets.NewString("keya", "keyb", "keyc", "keyd")
+	actual = sets.NewString(indexKeys...)
+	if !actual.Equal(expected) {
+		t.Errorf("expected %v does not match actual %v", expected, actual)
+	}
+	indexKeys, _ = store.IndexKeys("second", "value2")
+	expected = sets.NewString("keya", "keyb", "keyc", "keyd")
+	actual = sets.NewString(indexKeys...)
+	if !actual.Equal(expected) {
+		t.Errorf("expected %v does not match actual %v", expected, actual)
+	}
+}
+