diff --git a/src/Validator/Constraints/VatNumberValidator.php b/src/Validator/Constraints/VatNumberValidator.php
index 8a21446..4a9aba4 100644
--- a/src/Validator/Constraints/VatNumberValidator.php
+++ b/src/Validator/Constraints/VatNumberValidator.php
@@ -12,7 +12,7 @@
 
 class VatNumberValidator extends ConstraintValidator
 {
-    public function validate($value, Constraint $constraint)
+    public function validate($value, Constraint $constraint) : void
     {
         if (!$constraint instanceof VatNumber) {
             throw new UnexpectedTypeException($constraint, VatNumber::class);