diff --git a/default.nix b/default.nix
index 45875a3..5d189f8 100644
--- a/default.nix
+++ b/default.nix
@@ -278,7 +278,7 @@ in
       dovecot = {
         userAttrs = mkOption {
           type = types.nullOr types.str;
-          default = "";
+          default = null;
           description = ''
             LDAP attributes to be retrieved during userdb lookups.