diff --git a/stderr.js.flow b/stderr.js.flow
new file mode 100644
index 0000000..25be231
--- /dev/null
+++ b/stderr.js.flow
@@ -0,0 +1,5 @@
+// @flow strict
+
+import { Chalk } from './index';
+
+declare module.exports: Chalk;
diff --git a/test/_flow.js b/test/_flow.js
index 2cf3cf2..94d2115 100644
--- a/test/_flow.js
+++ b/test/_flow.js
@@ -1,5 +1,6 @@
 // @flow
 import chalk from '..';
+import cherr from '../stderr';
 
 // $ExpectError (Can't have typo in option name)
 chalk.constructor({levl: 1});
@@ -13,6 +14,10 @@ new chalk.constructor({enabled: true});
 chalk.underline(null);
 chalk.underline('foo');
 
+// $ExpectError (Can't pass in null)
+cherr.underline(null);
+cherr.underline('foo');
+
 // $ExpectError (Can't have typo in chalk method)
 chalk.rd('foo');
 chalk.red('foo');