diff --git a/libraries/classes/Plugins/Auth/AuthenticationCookie.php b/libraries/classes/Plugins/Auth/AuthenticationCookie.php
index 96e723c878..456699d171 100644
--- a/libraries/classes/Plugins/Auth/AuthenticationCookie.php
+++ b/libraries/classes/Plugins/Auth/AuthenticationCookie.php
@@ -335,8 +335,11 @@ class AuthenticationCookie extends AuthenticationPlugin
             $this->user = Core::sanitizeMySQLUser($_POST['pma_username']);
 
             $password = $_POST['pma_password'] ?? '';
-            if (strlen($password) > 256) {
-                $password = substr($password, 0, 256);
+            if (strlen($password) >= 1000) {
+                $conn_error = __('Your password is too long. To prevent denial-of-service attacks, ' .
+                    'phpMyAdmin restricts passwords to less than 1000 characters.');
+
+                return false;
             }
             $this->password = $password;