diff --git a/compiler/global/names.ml b/compiler/global/names.ml
index da0256d..20fec27 100644
--- a/compiler/global/names.ml
+++ b/compiler/global/names.ml
@@ -32,6 +32,7 @@
 
 type name = string
 type module_name = name
+type ack_name = name
 
 type modul =
   | Pervasives
diff --git a/compiler/heptagon/heptagon.ml b/compiler/heptagon/heptagon.ml
index 4498b66..26978f1 100644
--- a/compiler/heptagon/heptagon.ml
+++ b/compiler/heptagon/heptagon.ml
@@ -94,7 +94,7 @@ and op =
   | Econcat
   | Ereinit
 
-and ack = { ack_name : string; ack_params : static_exp list }
+and ack = { ack_name : ack_name; ack_params : static_exp list }
 
 and pat =
   | Etuplepat of pat list
diff --git a/compiler/heptagon/parsing/hept_parsetree.ml b/compiler/heptagon/parsing/hept_parsetree.ml
index d492af3..b701fea 100644
--- a/compiler/heptagon/parsing/hept_parsetree.ml
+++ b/compiler/heptagon/parsing/hept_parsetree.ml
@@ -41,6 +41,7 @@ type module_name = Names.modul
 (** state_names, [automata] translate them in constructors with a fresh type. *)
 type state_name = Names.name
 
+type ack_name = Names.ack_name
 
 type qualname =
   | Q of Names.qualname (* already qualified name *)
@@ -129,7 +130,7 @@ and op =
   | Econcat
   | Ereinit
 
-and ack = { ack_name: string; ack_params: static_exp list }
+and ack = { ack_name : ack_name; ack_params : static_exp list }
 
 and pat =
   | Etuplepat of pat list