diff --git a/Libraries/Components/ActivityIndicator/ActivityIndicator.js b/Libraries/Components/ActivityIndicator/ActivityIndicator.js
index 7438d1e35..65809a323 100644
--- a/Libraries/Components/ActivityIndicator/ActivityIndicator.js
+++ b/Libraries/Components/ActivityIndicator/ActivityIndicator.js
@@ -10,19 +10,15 @@
 
 'use strict';
 
-const ColorPropType = require('ColorPropType');
-const NativeMethodsMixin = require('NativeMethodsMixin');
 const Platform = require('Platform');
 const ProgressBarAndroid = require('ProgressBarAndroid');
-const PropTypes = require('prop-types');
 const React = require('React');
 const StyleSheet = require('StyleSheet');
 const View = require('View');
-const ViewPropTypes = require('ViewPropTypes');
 
-const createReactClass = require('create-react-class');
 const requireNativeComponent = require('requireNativeComponent');
 
+import type {NativeComponent} from 'ReactNative';
 import type {ViewProps} from 'ViewPropTypes';
 
 let RCTActivityIndicator;
@@ -31,113 +27,103 @@ const GRAY = '#999999';
 
 type IndicatorSize = number | 'small' | 'large';
 
+type IOSProps = $ReadOnly<{|
+  /**
+   * Whether the indicator should hide when not animating (true by default).
+   *
+   * See http://facebook.github.io/react-native/docs/activityindicator.html#hideswhenstopped
+   */
+  hidesWhenStopped?: ?boolean,
+|}>;
 type Props = $ReadOnly<{|
   ...ViewProps,
+  ...IOSProps,
 
+  /**
+   * Whether to show the indicator (true, the default) or hide it (false).
+   *
+   * See http://facebook.github.io/react-native/docs/activityindicator.html#animating
+   */
   animating?: ?boolean,
+
+  /**
+   * The foreground color of the spinner (default is gray).
+   *
+   * See http://facebook.github.io/react-native/docs/activityindicator.html#color
+   */
   color?: ?string,
-  hidesWhenStopped?: ?boolean,
+
+  /**
+   * Size of the indicator (default is 'small').
+   * Passing a number to the size prop is only supported on Android.
+   *
+   * See http://facebook.github.io/react-native/docs/activityindicator.html#size
+   */
   size?: ?IndicatorSize,
 |}>;
 
-type DefaultProps = {
-  animating: boolean,
-  color: ?string,
-  hidesWhenStopped: boolean,
-  size: IndicatorSize,
-};
-
 /**
  * Displays a circular loading indicator.
  *
  * See http://facebook.github.io/react-native/docs/activityindicator.html
  */
-const ActivityIndicator = ((createReactClass({
-  displayName: 'ActivityIndicator',
-  mixins: [NativeMethodsMixin],
+const ActivityIndicator = (
+  props: $ReadOnly<{|
+    ...Props,
+    forwardedRef?: ?React.Ref<'RCTActivityIndicatorView'>,
+  |}>,
+) => {
+  const {onLayout, style, forwardedRef, ...restProps} = props;
+  let sizeStyle;
 
-  propTypes: {
-    ...ViewPropTypes,
-    /**
-     * Whether to show the indicator (true, the default) or hide it (false).
-     *
-     * See http://facebook.github.io/react-native/docs/activityindicator.html#animating
-     */
-    animating: PropTypes.bool,
-    /**
-     * The foreground color of the spinner (default is gray).
-     *
-     * See http://facebook.github.io/react-native/docs/activityindicator.html#color
-     */
-    color: ColorPropType,
-    /**
-     * Size of the indicator (default is 'small').
-     * Passing a number to the size prop is only supported on Android.
-     *
-     * See http://facebook.github.io/react-native/docs/activityindicator.html#size
-     */
-    size: PropTypes.oneOfType([
-      PropTypes.oneOf(['small', 'large']),
-      PropTypes.number,
-    ]),
-    /**
-     * Whether the indicator should hide when not animating (true by default).
-     *
-     * @platform ios
-     *
-     * See http://facebook.github.io/react-native/docs/activityindicator.html#hideswhenstopped
-     */
-    hidesWhenStopped: PropTypes.bool,
-  },
+  switch (props.size) {
+    case 'small':
+      sizeStyle = styles.sizeSmall;
+      break;
+    case 'large':
+      sizeStyle = styles.sizeLarge;
+      break;
+    default:
+      sizeStyle = {height: props.size, width: props.size};
+      break;
+  }
 
-  getDefaultProps(): DefaultProps {
-    return {
-      animating: true,
-      color: Platform.OS === 'ios' ? GRAY : null,
-      hidesWhenStopped: true,
-      size: 'small',
-    };
-  },
+  const nativeProps = {
+    ...restProps,
+    ref: forwardedRef,
+    style: sizeStyle,
+    styleAttr: 'Normal',
+    indeterminate: true,
+  };
 
-  render() {
-    const {onLayout, style, ...props} = this.props;
-    let sizeStyle;
+  return (
+    <View onLayout={onLayout} style={[styles.container, style]}>
+      {Platform.OS === 'ios' ? (
+        <RCTActivityIndicator {...nativeProps} />
+      ) : (
+        <ProgressBarAndroid {...nativeProps} />
+      )}
+    </View>
+  );
+};
 
-    switch (props.size) {
-      case 'small':
-        sizeStyle = styles.sizeSmall;
-        break;
-      case 'large':
-        sizeStyle = styles.sizeLarge;
-        break;
-      default:
-        sizeStyle = {height: props.size, width: props.size};
-        break;
-    }
+// $FlowFixMe - TODO T29156721 `React.forwardRef` is not defined in Flow, yet.
+const ActivityIndicatorWithRef = React.forwardRef((props: Props, ref) => {
+  return <ActivityIndicator {...props} forwardedRef={ref} />;
+});
 
-    const nativeProps = {
-      ...props,
-      style: sizeStyle,
-      styleAttr: 'Normal',
-      indeterminate: true,
-    };
-
-    return (
-      <View onLayout={onLayout} style={[styles.container, style]}>
-        {Platform.OS === 'ios' ? (
-          <RCTActivityIndicator {...nativeProps} />
-        ) : (
-          <ProgressBarAndroid {...nativeProps} />
-        )}
-      </View>
-    );
-  },
-}): any): React.ComponentType<Props>);
+ActivityIndicatorWithRef.defaultProps = {
+  animating: true,
+  color: Platform.OS === 'ios' ? GRAY : null,
+  hidesWhenStopped: true,
+  size: 'small',
+};
+ActivityIndicatorWithRef.displayName = 'ActivityIndicator';
 
 if (Platform.OS === 'ios') {
   RCTActivityIndicator = requireNativeComponent(
     'RCTActivityIndicatorView',
-    ActivityIndicator,
+    null,
     {nativeOnly: {activityIndicatorViewStyle: true}},
   );
 }
@@ -157,4 +143,4 @@ const styles = StyleSheet.create({
   },
 });
 
-module.exports = ActivityIndicator;
+module.exports = (ActivityIndicatorWithRef: Class<NativeComponent<Props>>);
diff --git a/jest/mockComponent.js b/jest/mockComponent.js
index e22c34cca..6d5a80b47 100644
--- a/jest/mockComponent.js
+++ b/jest/mockComponent.js
@@ -20,9 +20,24 @@ module.exports = (moduleName, instanceMethods) => {
     render() {
       const name = RealComponent.displayName || RealComponent.name;
 
+      const props = Object.assign({}, RealComponent.defaultProps);
+
+      if (this.props) {
+        Object.keys(this.props).forEach(prop => {
+          // We can't just assign props on top of defaultProps
+          // because React treats undefined as special and different from null.
+          // If a prop is specified but set to undefined it is ignored and the
+          // default prop is used instead. If it is set to null, then the
+          // null value overwrites the default value.
+          if (this.props[prop] !== undefined) {
+            props[prop] = this.props[prop];
+          }
+        });
+      }
+
       return React.createElement(
         name.replace(/^(RCT|RK)/, ''),
-        this.props,
+        props,
         this.props.children,
       );
     }