diff --git a/src/base-term/Sidekick_base_term.ml b/src/base-term/Sidekick_base_term.ml
index 535ce45e..256b8a59 100644
--- a/src/base-term/Sidekick_base_term.ml
+++ b/src/base-term/Sidekick_base_term.ml
@@ -14,6 +14,7 @@ module Arg
     with type Term.t = Term.t
      and type Fun.t = Fun.t
      and type Ty.t = Ty.t
+     and type Term.state = Term.state
 = struct
   module Term = Term
   module Fun = Fun