diff --git a/otherlibs/stdune/id.ml b/otherlibs/stdune/id.ml
index 81d1f38f649..bf2df115a07 100644
--- a/otherlibs/stdune/id.ml
+++ b/otherlibs/stdune/id.ml
@@ -1,5 +1,5 @@
 module type S = sig
-  type t
+  type t [@@immediate]
 
   include Comparable_intf.S with type key := t
 
diff --git a/otherlibs/stdune/id.mli b/otherlibs/stdune/id.mli
index 8282a293fb0..2a6ad93da13 100644
--- a/otherlibs/stdune/id.mli
+++ b/otherlibs/stdune/id.mli
@@ -1,5 +1,5 @@
 module type S = sig
-  type t
+  type t [@@immediate]
 
   include Comparable_intf.S with type key := t