diff --git a/resources/interfaces/express.js b/resources/interfaces/express.js
index c465e72..82d0280 100644
--- a/resources/interfaces/express.js
+++ b/resources/interfaces/express.js
@@ -1,4 +1,4 @@
-/* @flow */
+/* @flow strict */
 /* Flow declarations for express requests and responses */
 /* eslint-disable no-unused-vars */
 declare class Request {
diff --git a/src/__tests__/http-test.js b/src/__tests__/http-test.js
index a83af96..6dab430 100644
--- a/src/__tests__/http-test.js
+++ b/src/__tests__/http-test.js
@@ -1,4 +1,3 @@
-/* @flow */
 /**
  *  Copyright (c) 2015-present, Facebook, Inc.
  *  All rights reserved.
@@ -6,6 +5,8 @@
  *  This source code is licensed under the BSD-style license found in the
  *  LICENSE file in the root directory of this source tree. An additional grant
  *  of patent rights can be found in the PATENTS file in the same directory.
+ *
+ *  @flow strict
  */
 
 // 80+ char lines are useful in describe/it, so ignore in this file.
diff --git a/src/index.js b/src/index.js
index 2049ae2..5ff1424 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,4 +1,3 @@
-/* @flow */
 /**
  *  Copyright (c) 2015-present, Facebook, Inc.
  *  All rights reserved.
@@ -6,6 +5,8 @@
  *  This source code is licensed under the BSD-style license found in the
  *  LICENSE file in the root directory of this source tree. An additional grant
  *  of patent rights can be found in the PATENTS file in the same directory.
+ *
+ *  @flow strict
  */
 
 import accepts from 'accepts';
diff --git a/src/parseBody.js b/src/parseBody.js
index cdec841..0cd8726 100644
--- a/src/parseBody.js
+++ b/src/parseBody.js
@@ -1,4 +1,3 @@
-/* @flow */
 /**
  *  Copyright (c) 2015-present, Facebook, Inc.
  *  All rights reserved.
@@ -6,6 +5,8 @@
  *  This source code is licensed under the BSD-style license found in the
  *  LICENSE file in the root directory of this source tree. An additional grant
  *  of patent rights can be found in the PATENTS file in the same directory.
+ *
+ *  @flow strict
  */
 
 import contentType from 'content-type';
diff --git a/src/renderGraphiQL.js b/src/renderGraphiQL.js
index cfff80b..c3bba12 100644
--- a/src/renderGraphiQL.js
+++ b/src/renderGraphiQL.js
@@ -1,4 +1,3 @@
-/* @flow */
 /**
  *  Copyright (c) 2015-present, Facebook, Inc.
  *  All rights reserved.
@@ -6,6 +5,8 @@
  *  This source code is licensed under the BSD-style license found in the
  *  LICENSE file in the root directory of this source tree. An additional grant
  *  of patent rights can be found in the PATENTS file in the same directory.
+ *
+ *  @flow strict
  */
 
 type GraphiQLData = {