diff --git a/heptagon/analysis/interface.ml b/heptagon/analysis/interface.ml
index 184a658..5f4ac72 100644
--- a/heptagon/analysis/interface.ml
+++ b/heptagon/analysis/interface.ml
@@ -21,8 +21,9 @@ module Type =
   struct
     let sigtype { sig_name = name; sig_inputs = i_list; 
                   sig_outputs = o_list; sig_params = params } =
-	      name, { node_inputs = i_list;
-		            node_outputs = o_list;
+      let check_arg a = { a with a_type = check_type a.a_type } in
+	      name, { node_inputs = List.map check_arg i_list;
+		            node_outputs = List.map check_arg o_list;
 		            node_params = params;
 		            node_params_constraints = []; }