diff --git a/src/pvec/containers_pvec.mli b/src/pvec/containers_pvec.mli
index bee50bec..2d3a815c 100644
--- a/src/pvec/containers_pvec.mli
+++ b/src/pvec/containers_pvec.mli
@@ -9,8 +9,17 @@
 *)
 
 type 'a iter = ('a -> unit) -> unit
+
+[@@@ifge 5.0]
+
 type !'a t
 
+[@@@else_]
+
+type 'a t
+
+[@@@endif]
+
 val empty : 'a t
 (** Empty vector. *)