diff --git a/postfixadmin.nix b/postfixadmin.nix
index c7aec6a..b4dd9d3 100644
--- a/postfixadmin.nix
+++ b/postfixadmin.nix
@@ -15,7 +15,7 @@ in
   users.users."${pfaUser}" = {
     isSystemUser = true;
     group = "${pfaGroup}";
-    extraGroups = "dovecot2";
+    extraGroups = [ "dovecot2" ];
     description = "PHP User for postfixadmin";
   };