diff --git a/server/plugins-available/mail_plugin_dkim.inc.php b/server/plugins-available/mail_plugin_dkim.inc.php
index 8edd657246b8e5dc885c3efdee251620c9b2d062..e07dfe8af0115eac39ef0fcda80b9671881e1342 100644
--- a/server/plugins-available/mail_plugin_dkim.inc.php
+++ b/server/plugins-available/mail_plugin_dkim.inc.php
@@ -128,7 +128,7 @@ class mail_plugin_dkim {
 					$amavis_user=rtrim($amavis_user, ":");
 					mkdir($mail_config['dkim_path'], 0750, true);
 					exec('chown '.$amavis_user.' /var/lib/amavis/dkim');
-					unset $amavis_user;
+					unset($amavis_user);
 				} else {
 					mkdir($mail_config['dkim_path'], 0755, true);
 				}