diff --git a/src/Authentication/Passwords/NothingPersonalValidator.php b/src/Authentication/Passwords/NothingPersonalValidator.php
index 8d7f6d07d..d97b962b1 100644
--- a/src/Authentication/Passwords/NothingPersonalValidator.php
+++ b/src/Authentication/Passwords/NothingPersonalValidator.php
@@ -95,7 +95,7 @@ protected function isNotPersonal(string $password, ?User $user): bool
 
             foreach ($personalFields as $value) {
                 if (! empty($user->{$value})) {
-                    $needles[] = strtolower($user->{$value});
+                    $needles[] = strtolower((string) $user->{$value});
                 }
             }