diff --git a/src/renderers/shared/stack/reconciler/ReactInstanceType.js b/src/renderers/shared/stack/reconciler/ReactInstanceType.js
index 36b2bd0d5d..b27d3371c7 100644
--- a/src/renderers/shared/stack/reconciler/ReactInstanceType.js
+++ b/src/renderers/shared/stack/reconciler/ReactInstanceType.js
@@ -24,8 +24,8 @@ export type ReactInstance = {
   receiveComponent: any,
   performUpdateIfNecessary: any,
   updateComponent: any,
-  attachRef: any,
-  detachRef: any,
+  attachRef: (ref: string, component: ReactInstance) => void,
+  detachRef: (ref: string) => void,
   getName: () => string,
   getPublicInstance: any,
 
diff --git a/src/renderers/shared/stack/reconciler/ReactOwner.js b/src/renderers/shared/stack/reconciler/ReactOwner.js
index df2bfb8d7b..270f7fb933 100644
--- a/src/renderers/shared/stack/reconciler/ReactOwner.js
+++ b/src/renderers/shared/stack/reconciler/ReactOwner.js
@@ -7,12 +7,28 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ReactOwner
+ * @flow
  */
 
 'use strict';
 
 var invariant = require('invariant');
 
+import type { ReactInstance } from 'ReactInstanceType';
+
+/**
+ * @param {?object} object
+ * @return {boolean} True if `object` is a valid owner.
+ * @final
+ */
+function isValidOwner(object: any): bool {
+  return !!(
+    object &&
+    typeof object.attachRef === 'function' &&
+    typeof object.detachRef === 'function'
+  );
+}
+
 /**
  * ReactOwners are capable of storing references to owned components.
  *
@@ -44,20 +60,6 @@ var invariant = require('invariant');
  * @class ReactOwner
  */
 var ReactOwner = {
-
-  /**
-   * @param {?object} object
-   * @return {boolean} True if `object` is a valid owner.
-   * @final
-   */
-  isValidOwner: function(object) {
-    return !!(
-      object &&
-      typeof object.attachRef === 'function' &&
-      typeof object.detachRef === 'function'
-    );
-  },
-
   /**
    * Adds a component by ref to an owner component.
    *
@@ -67,9 +69,13 @@ var ReactOwner = {
    * @final
    * @internal
    */
-  addComponentAsRefTo: function(component, ref, owner) {
+  addComponentAsRefTo: function(
+    component: ReactInstance,
+    ref: string,
+    owner: ReactInstance,
+  ): void {
     invariant(
-      ReactOwner.isValidOwner(owner),
+      isValidOwner(owner),
       'addComponentAsRefTo(...): Only a ReactOwner can have refs. You might ' +
       'be adding a ref to a component that was not created inside a component\'s ' +
       '`render` method, or you have multiple copies of React loaded ' +
@@ -87,9 +93,13 @@ var ReactOwner = {
    * @final
    * @internal
    */
-  removeComponentAsRefFrom: function(component, ref, owner) {
+  removeComponentAsRefFrom: function(
+    component: ReactInstance,
+    ref: string,
+    owner: ReactInstance,
+  ): void {
     invariant(
-      ReactOwner.isValidOwner(owner),
+      isValidOwner(owner),
       'removeComponentAsRefFrom(...): Only a ReactOwner can have refs. You might ' +
       'be removing a ref to a component that was not created inside a component\'s ' +
       '`render` method, or you have multiple copies of React loaded ' +