diff --git a/src/BusProNet/Model/ProfileResponse.php b/src/BusProNet/Model/ProfileResponse.php
index 183f14e..b6591eb 100644
--- a/src/BusProNet/Model/ProfileResponse.php
+++ b/src/BusProNet/Model/ProfileResponse.php
@@ -99,7 +99,7 @@ class ProfileResponse
         return $this;
     }
 
-    public function getDateOfBirth(): \DateTimeImmutable
+    public function getDateOfBirth(): ?\DateTimeImmutable
     {
         return $this->dateOfBirth;
     }