diff --git a/cookbook/validation/custom_constraint.rst b/cookbook/validation/custom_constraint.rst
index 68e2f464639..a248a8494aa 100644
--- a/cookbook/validation/custom_constraint.rst
+++ b/cookbook/validation/custom_constraint.rst
@@ -64,7 +64,7 @@ The validator class is also simple, and only has one required method ``validate(
     {
         public function validate($value, Constraint $constraint)
         {
-            if (!preg_match('/^[a-zA-Za0-9]+$/', $value, $matches)) {
+            if (!preg_match('/^[a-zA-Z0-9]+$/', $value, $matches)) {
                 // If you're using the new 2.5 validation API (you probably are!)
                 $this->context->buildViolation($constraint->message)
                     ->setParameter('%string%', $value)