diff --git a/Libraries/Components/AccessibilityInfo/AccessibilityInfo.android.js b/Libraries/Components/AccessibilityInfo/AccessibilityInfo.android.js
index 09547ea06..420d0380a 100644
--- a/Libraries/Components/AccessibilityInfo/AccessibilityInfo.android.js
+++ b/Libraries/Components/AccessibilityInfo/AccessibilityInfo.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/CheckBox/CheckBox.android.js b/Libraries/Components/CheckBox/CheckBox.android.js
index 0c7f13dec..e02201348 100644
--- a/Libraries/Components/CheckBox/CheckBox.android.js
+++ b/Libraries/Components/CheckBox/CheckBox.android.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 'use strict';
diff --git a/Libraries/Components/DatePickerAndroid/DatePickerAndroid.android.js b/Libraries/Components/DatePickerAndroid/DatePickerAndroid.android.js
index bd91263a8..c8f7fb843 100644
--- a/Libraries/Components/DatePickerAndroid/DatePickerAndroid.android.js
+++ b/Libraries/Components/DatePickerAndroid/DatePickerAndroid.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/MaskedView/MaskedViewIOS.android.js b/Libraries/Components/MaskedView/MaskedViewIOS.android.js
index 49d44e154..1e779382f 100644
--- a/Libraries/Components/MaskedView/MaskedViewIOS.android.js
+++ b/Libraries/Components/MaskedView/MaskedViewIOS.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/Picker/PickerAndroid.android.js b/Libraries/Components/Picker/PickerAndroid.android.js
index 1f80aa392..135301eff 100644
--- a/Libraries/Components/Picker/PickerAndroid.android.js
+++ b/Libraries/Components/Picker/PickerAndroid.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/ProgressBarAndroid/ProgressBarAndroid.android.js b/Libraries/Components/ProgressBarAndroid/ProgressBarAndroid.android.js
index f343e2e54..856f7116b 100644
--- a/Libraries/Components/ProgressBarAndroid/ProgressBarAndroid.android.js
+++ b/Libraries/Components/ProgressBarAndroid/ProgressBarAndroid.android.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Components/SafeAreaView/SafeAreaView.android.js b/Libraries/Components/SafeAreaView/SafeAreaView.android.js
index a581258a5..f730bc6ab 100644
--- a/Libraries/Components/SafeAreaView/SafeAreaView.android.js
+++ b/Libraries/Components/SafeAreaView/SafeAreaView.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/StatusBar/StatusBarIOS.android.js b/Libraries/Components/StatusBar/StatusBarIOS.android.js
index 96f77d786..fc8b4b70d 100644
--- a/Libraries/Components/StatusBar/StatusBarIOS.android.js
+++ b/Libraries/Components/StatusBar/StatusBarIOS.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/TabBarIOS/TabBarIOS.android.js b/Libraries/Components/TabBarIOS/TabBarIOS.android.js
index e8e376f8a..06dfe10db 100644
--- a/Libraries/Components/TabBarIOS/TabBarIOS.android.js
+++ b/Libraries/Components/TabBarIOS/TabBarIOS.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/TimePickerAndroid/TimePickerAndroid.android.js b/Libraries/Components/TimePickerAndroid/TimePickerAndroid.android.js
index 6cdd964cc..139ffa161 100644
--- a/Libraries/Components/TimePickerAndroid/TimePickerAndroid.android.js
+++ b/Libraries/Components/TimePickerAndroid/TimePickerAndroid.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/ToastAndroid/ToastAndroid.android.js b/Libraries/Components/ToastAndroid/ToastAndroid.android.js
index c661adf50..a259c17a0 100644
--- a/Libraries/Components/ToastAndroid/ToastAndroid.android.js
+++ b/Libraries/Components/ToastAndroid/ToastAndroid.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Components/ViewPager/ViewPagerAndroid.android.js b/Libraries/Components/ViewPager/ViewPagerAndroid.android.js
index 2ccdd31b5..a3ca76742 100644
--- a/Libraries/Components/ViewPager/ViewPagerAndroid.android.js
+++ b/Libraries/Components/ViewPager/ViewPagerAndroid.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Image/Image.android.js b/Libraries/Image/Image.android.js
index d0e685a5e..ea229e0b4 100644
--- a/Libraries/Image/Image.android.js
+++ b/Libraries/Image/Image.android.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/Libraries/Network/RCTNetworking.android.js b/Libraries/Network/RCTNetworking.android.js
index 85db7ed6f..13e9ded6d 100644
--- a/Libraries/Network/RCTNetworking.android.js
+++ b/Libraries/Network/RCTNetworking.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Sample/Sample.android.js b/Libraries/Sample/Sample.android.js
index 2755a884b..e67090974 100644
--- a/Libraries/Sample/Sample.android.js
+++ b/Libraries/Sample/Sample.android.js
@@ -7,7 +7,7 @@
  * Stub of Sample for Android.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Settings/Settings.android.js b/Libraries/Settings/Settings.android.js
index 1e6708a18..98e512ec6 100644
--- a/Libraries/Settings/Settings.android.js
+++ b/Libraries/Settings/Settings.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Utilities/HMRLoadingView.android.js b/Libraries/Utilities/HMRLoadingView.android.js
index ae1763653..43454739b 100644
--- a/Libraries/Utilities/HMRLoadingView.android.js
+++ b/Libraries/Utilities/HMRLoadingView.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Utilities/Platform.android.js b/Libraries/Utilities/Platform.android.js
index 92edba182..d5b3d41ff 100644
--- a/Libraries/Utilities/Platform.android.js
+++ b/Libraries/Utilities/Platform.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/Libraries/Utilities/PlatformOS.android.js b/Libraries/Utilities/PlatformOS.android.js
index 5ddf8d81e..fae79f357 100644
--- a/Libraries/Utilities/PlatformOS.android.js
+++ b/Libraries/Utilities/PlatformOS.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/RNTester/js/PermissionsExampleAndroid.android.js b/RNTester/js/PermissionsExampleAndroid.android.js
index 81a7ec5b1..7a7d72cd8 100644
--- a/RNTester/js/PermissionsExampleAndroid.android.js
+++ b/RNTester/js/PermissionsExampleAndroid.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/RNTester/js/ProgressBarAndroidExample.android.js b/RNTester/js/ProgressBarAndroidExample.android.js
index 2b3d7feea..78e754599 100644
--- a/RNTester/js/ProgressBarAndroidExample.android.js
+++ b/RNTester/js/ProgressBarAndroidExample.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/RNTester/js/RNTesterApp.android.js b/RNTester/js/RNTesterApp.android.js
index 42c43b81a..0c7838e29 100644
--- a/RNTester/js/RNTesterApp.android.js
+++ b/RNTester/js/RNTesterApp.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/RNTester/js/RNTesterList.android.js b/RNTester/js/RNTesterList.android.js
index 8e8f6b791..b57f33133 100644
--- a/RNTester/js/RNTesterList.android.js
+++ b/RNTester/js/RNTesterList.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/RNTester/js/TextExample.android.js b/RNTester/js/TextExample.android.js
index e38a92702..b9afb3793 100644
--- a/RNTester/js/TextExample.android.js
+++ b/RNTester/js/TextExample.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/RNTester/js/TextInputExample.android.js b/RNTester/js/TextInputExample.android.js
index 30cee2eb2..4c143207d 100644
--- a/RNTester/js/TextInputExample.android.js
+++ b/RNTester/js/TextInputExample.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/RNTester/js/ToastAndroidExample.android.js b/RNTester/js/ToastAndroidExample.android.js
index 80ea97715..ec8c5cb25 100644
--- a/RNTester/js/ToastAndroidExample.android.js
+++ b/RNTester/js/ToastAndroidExample.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/RNTester/js/ToolbarAndroidExample.android.js b/RNTester/js/ToolbarAndroidExample.android.js
index 4043c054f..adc44cf44 100644
--- a/RNTester/js/ToolbarAndroidExample.android.js
+++ b/RNTester/js/ToolbarAndroidExample.android.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  */
 
 'use strict';
diff --git a/flow/Map.js b/flow/Map.js
index 0723ea426..7b6c095d0 100644
--- a/flow/Map.js
+++ b/flow/Map.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/flow/Position.js b/flow/Position.js
index 5bd2717c0..2886fb69e 100644
--- a/flow/Position.js
+++ b/flow/Position.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @nolint
  * @format
  */
diff --git a/flow/Promise.js b/flow/Promise.js
index 64350cabc..cde3a9d59 100644
--- a/flow/Promise.js
+++ b/flow/Promise.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/flow/Set.js b/flow/Set.js
index ea3b1533b..f135bf3bf 100644
--- a/flow/Set.js
+++ b/flow/Set.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @nolint
  * @format
  */
diff --git a/flow/Stringish.js b/flow/Stringish.js
index 55d0e3707..4ee9120bb 100644
--- a/flow/Stringish.js
+++ b/flow/Stringish.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/flow/console.js b/flow/console.js
index a5d0d31bf..69b2ba7d6 100644
--- a/flow/console.js
+++ b/flow/console.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/flow/create-react-class.js b/flow/create-react-class.js
index dc3fea97e..c7cf3c847 100644
--- a/flow/create-react-class.js
+++ b/flow/create-react-class.js
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow
+ * @flow strict
  * @nolint
  */
 
diff --git a/flow/jest.js b/flow/jest.js
index ebd7c9ec0..336c88383 100644
--- a/flow/jest.js
+++ b/flow/jest.js
@@ -18,7 +18,7 @@
  *  - added JestMockFn.mock.thrownErrors
  *  - added JestMockFn.mock.returnValues
  *  - added jest.setTimeout
- * @flow
+ * @flow strict
  * @format
  */
 
diff --git a/flow/prop-types.js b/flow/prop-types.js
index be239f5bd..5236a762c 100644
--- a/flow/prop-types.js
+++ b/flow/prop-types.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  * @nolint
  * @format
  */