diff --git a/nixos/modules/services/mail/mailman.nix b/nixos/modules/services/mail/mailman.nix
index 15f5d75df8a..e917209f3d1 100644
--- a/nixos/modules/services/mail/mailman.nix
+++ b/nixos/modules/services/mail/mailman.nix
@@ -109,7 +109,7 @@ in {
       };
 
       webHosts = mkOption {
-        type = types.listOf types.string;
+        type = types.listOf types.str;
         default = [];
         description = ''
           The list of hostnames and/or IP addresses from which the Mailman Web