diff --git a/mock/src/shims.d.ts b/mock/src/shims.d.ts
index 50dc749..e5a4266 100644
--- a/mock/src/shims.d.ts
+++ b/mock/src/shims.d.ts
@@ -2,7 +2,7 @@
 
 declare namespace NodeJS {
   export interface ProcessEnv {
-    NODE_ENV: string;
+    NODE_ENV: 'development' | 'production';
 
     HOST: string;
     PORT: number;