diff --git a/app/User/UseCases/CreateUser.php b/app/User/UseCases/CreateUser.php
index e2b9b55..cfec430 100644
--- a/app/User/UseCases/CreateUser.php
+++ b/app/User/UseCases/CreateUser.php
@@ -21,8 +21,13 @@ class CreateUser
             throw new BadRequestException('email is required');
         }
 
+        $email = new EmailAddress($dto->email);
+        if ($this->userRepo->findByEmail($email) !== null) {
+            throw new BadRequestException('email already taken');
+        }
+
         $this->userRepo->create(new CreateUserDto(
-            email: new EmailAddress($dto->email),
+            email: $email,
             isAdmin: $dto->isAdmin,
         ));
     }