diff --git a/packages/caldav.0.2.99~dev/opam b/packages/caldav.0.2.99~dev/opam
index d517bb5..6d54924 100644
--- a/packages/caldav.0.2.99~dev/opam
+++ b/packages/caldav.0.2.99~dev/opam
@@ -36,7 +36,7 @@ depends: [
   "ptime" {>= "0.8.5"}
   "cohttp" {>= "2.0.0"}
   "cohttp-lwt" {>= "2.0.0"}
-  "cohttp-lwt-unix" {with-test & >= "2.0.0"}
+  "cohttp-lwt-unix" {with-test & >= "2.0.0" & < "6.0.0~~"}
   "digestif" {>= "1.2.0"}
   "mirage-crypto-rng" {>= "1.0.0"}
   "mirage-crypto-rng-mirage" {>= "1.0.0"}