diff --git a/expander/str_generate_sexp_grammar.ml b/expander/str_generate_sexp_grammar.ml
index 90e8690..38ca565 100644
--- a/expander/str_generate_sexp_grammar.ml
+++ b/expander/str_generate_sexp_grammar.ml
@@ -5,6 +5,11 @@ open! Sexp.Private.Raw_grammar
 module Var_name  = String
 module Type_name = String
 
+module Longident = struct
+  include Longident
+  include (val Comparator.make ~compare ~sexp_of_t)
+end
+
 let debug_s message values =
   Caml.prerr_endline (Sexp.to_string_hum (Sexp.message message values))
 ;;