diff --git a/default.nix b/default.nix
index 6bd499c..45875a3 100644
--- a/default.nix
+++ b/default.nix
@@ -277,7 +277,7 @@ in
 
       dovecot = {
         userAttrs = mkOption {
-          type = types.str;
+          type = types.nullOr types.str;
           default = "";
           description = ''
             LDAP attributes to be retrieved during userdb lookups.
diff --git a/mail-server/dovecot.nix b/mail-server/dovecot.nix
index a6251fd..11f2708 100644
--- a/mail-server/dovecot.nix
+++ b/mail-server/dovecot.nix
@@ -76,7 +76,7 @@ let
       auth_bind = yes
       base = ${cfg.ldap.searchBase}
       scope = ${mkLdapSearchScope cfg.ldap.searchScope}
-      ${lib.optionalString (cfg.ldap.dovecot.userAttrs != "") ''
+      ${lib.optionalString (cfg.ldap.dovecot.userAttrs != null) ''
       user_attrs = ${cfg.ldap.dovecot.userAttrs}
       ''}
       user_filter = ${cfg.ldap.dovecot.userFilter}