diff --git a/packages/KaSim/KaSim.4.0.0/opam b/packages/KaSim/KaSim.4.0.0/opam
index d15110d0dff5..b66629d869ec 100644
--- a/packages/KaSim/KaSim.4.0.0/opam
+++ b/packages/KaSim/KaSim.4.0.0/opam
@@ -15,7 +15,7 @@ depends: [
   "ocamlfind"
   "ocamlbuild" {build}
   "yojson" {>= "1.1.3" & < "2.0.0"}
-  "lwt"
+  "lwt" {< "4.0.0"}
 ]
 depopts: [
   "labltk" "cohttp-lwt-unix"