diff --git a/pkgs/lib/modules.nix b/pkgs/lib/modules.nix
index f0638da3c00..19b04bd827f 100644
--- a/pkgs/lib/modules.nix
+++ b/pkgs/lib/modules.nix
@@ -219,7 +219,7 @@ rec {
                     }) (definitionsOf name);
 
                   config = builtins.tryEval
-                    (lib.getAttr name result.config);
+                    (builtins.toXML (lib.getAttr name result.config));
                 }
             else if all isAttrs values then
               (recurseInto name modules).options