diff --git a/README.md b/README.md
index 20d2fcf..599a6cd 100644
--- a/README.md
+++ b/README.md
@@ -874,7 +874,7 @@ if (isEmailNotUsed(email)) {
 **Good:**
 
 ```ts
-function isEmailUsed(email): boolean {
+function isEmailUsed(email: string): boolean {
   // ...
 }