diff --git a/flow-typed/npm/debug_v2.x.x.js b/flow-typed/npm/debug_v2.x.x.js
index c104d8aaec..675c2fe6fc 100644
--- a/flow-typed/npm/debug_v2.x.x.js
+++ b/flow-typed/npm/debug_v2.x.x.js
@@ -11,10 +11,18 @@
 // https://github.com/visionmedia/debug
 // https://www.npmjs.com/package/debug
 
+interface DebugFN {
+  (...args: Array<mixed>): void;
+  enable(match: string): void;
+  disable(): void;
+  enabled: () => boolean;
+}
+
 declare module 'debug' {
   declare module.exports: {
-    (namespace: string): (...Array<mixed>) => void,
+    (namespace: string): DebugFN,
     enable(match: string): void,
     disable(): void,
+    enabled: () => boolean,
   };
 }
diff --git a/packages/metro/src/__mocks__/debug.js b/packages/metro/src/__mocks__/debug.js
index 8a7792494d..8f5c75b287 100644
--- a/packages/metro/src/__mocks__/debug.js
+++ b/packages/metro/src/__mocks__/debug.js
@@ -10,8 +10,15 @@
 
 'use strict';
 
-function debug(namespace: string): (...Array<mixed>) => void {
-  return () => {};
+interface DebugFN {
+  (...args: Array<mixed>): void;
+  enabled: () => boolean;
+}
+
+function debug(namespace: string): DebugFN {
+  const fn = (...args: Array<mixed>) => {};
+  fn.enabled = () => false;
+  return fn;
 }
 
 debug.enable = (match: string) => {};