diff --git a/packages/h1_parser/h1_parser.0.0.2/opam b/packages/h1_parser/h1_parser.0.0.2/opam
index 5b49eed9e8e1..1ed14a8f0839 100644
--- a/packages/h1_parser/h1_parser.0.0.2/opam
+++ b/packages/h1_parser/h1_parser.0.0.2/opam
@@ -20,6 +20,9 @@ depends: [
   "ppx_assert" {with-test}
   "odoc" {with-doc}
 ]
+conflicts: [
+  "cohttp-lwt-unix" {with-test & >= "5.0.0"}
+]
 build: [
   ["dune" "subst"] {dev}
   [
diff --git a/packages/ocsigenserver/ocsigenserver.3.0.0/opam b/packages/ocsigenserver/ocsigenserver.3.0.0/opam
index b8ecec90a1f9..f0a190dd00c5 100644
--- a/packages/ocsigenserver/ocsigenserver.3.0.0/opam
+++ b/packages/ocsigenserver/ocsigenserver.3.0.0/opam
@@ -52,7 +52,7 @@ depends: [
   "cryptokit"
   "dbm" | "sqlite3" | "pgocaml"
   "ipaddr" {>= "2.1"}
-  "cohttp-lwt-unix"
+  "cohttp-lwt-unix" {< "5.0.0"}
   "conduit-lwt-unix" {>= "2.0.0"}
   "hmap"
   "xml-light"
diff --git a/packages/ocsigenserver/ocsigenserver.4.0.1/opam b/packages/ocsigenserver/ocsigenserver.4.0.1/opam
index 366d68e0688a..9870e41a8e55 100644
--- a/packages/ocsigenserver/ocsigenserver.4.0.1/opam
+++ b/packages/ocsigenserver/ocsigenserver.4.0.1/opam
@@ -56,7 +56,7 @@ depends: [
   "cryptokit"
   "dbm" | "sqlite3" | "pgocaml"
   "ipaddr" {>= "2.1"}
-  "cohttp-lwt-unix"
+  "cohttp-lwt-unix" {< "5.0.0"}
   "conduit-lwt-unix" {>= "2.0.0"}
   "hmap"
   "xml-light"
diff --git a/packages/ocsigenserver/ocsigenserver.4.0.2/opam b/packages/ocsigenserver/ocsigenserver.4.0.2/opam
index fb90152577d2..c1f1a1b74423 100644
--- a/packages/ocsigenserver/ocsigenserver.4.0.2/opam
+++ b/packages/ocsigenserver/ocsigenserver.4.0.2/opam
@@ -56,7 +56,7 @@ depends: [
   "cryptokit"
   "dbm" | "sqlite3" | "pgocaml"
   "ipaddr" {>= "2.1"}
-  "cohttp-lwt-unix"
+  "cohttp-lwt-unix" {< "5.0.0"}
   "conduit-lwt-unix" {>= "2.0.0"}
   "hmap"
   "xml-light"
diff --git a/packages/ocsigenserver/ocsigenserver.5.0.0/opam b/packages/ocsigenserver/ocsigenserver.5.0.0/opam
index 277745b39187..59f5f0ee42dd 100644
--- a/packages/ocsigenserver/ocsigenserver.5.0.0/opam
+++ b/packages/ocsigenserver/ocsigenserver.5.0.0/opam
@@ -56,7 +56,7 @@ depends: [
   "cryptokit"
   "dbm" | "sqlite3" | "pgocaml"
   "ipaddr" {>= "2.1"}
-  "cohttp-lwt-unix"
+  "cohttp-lwt-unix" {< "5.0.0"}
   "conduit-lwt-unix" {>= "2.0.0"}
   "hmap"
   "xml-light"
diff --git a/packages/podge/podge.0.2/opam b/packages/podge/podge.0.2/opam
index cfc817d6cfd6..3ce2b7b432cf 100644
--- a/packages/podge/podge.0.2/opam
+++ b/packages/podge/podge.0.2/opam
@@ -19,7 +19,7 @@ remove: ["ocamlfind" "remove" "podge"]
 depends: [
   "ocaml" {>= "4.02.2"}
   "base-unix"
-  "cohttp" {>= "0.9.7"}
+  "cohttp" {>= "0.9.7" & < "5.0.0"}
   "oasis" {build & >= "0.4"}
   "ocamlfind" {build}
   "tyxml" {< "4.0.0"}
diff --git a/packages/podge/podge.0.3/opam b/packages/podge/podge.0.3/opam
index af82dc0c4e49..474c9f941a87 100644
--- a/packages/podge/podge.0.3/opam
+++ b/packages/podge/podge.0.3/opam
@@ -18,7 +18,7 @@ remove: ["ocamlfind" "remove" "podge"]
 depends: [
   "ocaml" {>= "4.02.1"}
   "base-unix"
-  "cohttp" {>= "0.9.7"}
+  "cohttp" {>= "0.9.7" & < "5.0.0"}
   "oasis" {build & >= "0.4"}
   "ocamlfind" {build}
   "re" {>= "1.3.0"}
diff --git a/packages/reddit_api_async/reddit_api_async.0.1.0/opam b/packages/reddit_api_async/reddit_api_async.0.1.0/opam
index 005dd9963917..019fd58c2306 100644
--- a/packages/reddit_api_async/reddit_api_async.0.1.0/opam
+++ b/packages/reddit_api_async/reddit_api_async.0.1.0/opam
@@ -10,7 +10,7 @@ depends: [
   "dune" {>= "2.5"}
   "async" {>= "v0.14.0"}
   "async_ssl" {>= "v0.14.0"}
-  "cohttp-async" {>= "2.5.4"}
+  "cohttp-async" {>= "2.5.4" & < "5.0.0"}
   "core" {>= "v0.14.0"}
   "ezjsonm" {>= "1.0"}
   "reddit_api_kernel" {= version}
diff --git a/packages/reddit_api_async/reddit_api_async.0.1.1/opam b/packages/reddit_api_async/reddit_api_async.0.1.1/opam
index d4c19a1fac40..15b27c7a8599 100644
--- a/packages/reddit_api_async/reddit_api_async.0.1.1/opam
+++ b/packages/reddit_api_async/reddit_api_async.0.1.1/opam
@@ -10,7 +10,7 @@ depends: [
   "dune" {>= "2.5"}
   "async" {>= "v0.14.0"}
   "async_ssl" {>= "v0.14.0"}
-  "cohttp-async" {>= "2.5.4"}
+  "cohttp-async" {>= "2.5.4" & < "5.0.0"}
   "core" {>= "v0.14.0"}
   "ezjsonm" {>= "1.0"}
   "reddit_api_kernel" {= version}
diff --git a/packages/websocket-lwt-unix/websocket-lwt-unix.2.14/opam b/packages/websocket-lwt-unix/websocket-lwt-unix.2.14/opam
index 737709b632ee..16e938ac764b 100644
--- a/packages/websocket-lwt-unix/websocket-lwt-unix.2.14/opam
+++ b/packages/websocket-lwt-unix/websocket-lwt-unix.2.14/opam
@@ -5,6 +5,7 @@ homepage: "https://github.com/vbmithr/ocaml-websocket"
 bug-reports: "https://github.com/vbmithr/ocaml-websocket/issues"
 dev-repo: "git+https://github.com/vbmithr/ocaml-websocket"
 doc: "https://vbmithr.github.io/ocaml-websocket/doc"
+license: "ISC"
 tags: [
   "org:mirage"
   "org:xapi-project"
@@ -15,7 +16,7 @@ depends: [
   "dune" {>= "1.3.0"}
   "websocket" {= version}
   "lwt_log" {>= "1.1.1"}
-  "cohttp-lwt-unix" {>= "2.5.1"}
+  "cohttp-lwt-unix" {>= "2.5.1" & < "5.0.0"}
 ]
 synopsis: "Websocket library (Lwt)"
 description: """
diff --git a/packages/zeit/zeit.0.1.0/opam b/packages/zeit/zeit.0.1.0/opam
index 41a065747a76..9a9f0a1ed770 100644
--- a/packages/zeit/zeit.0.1.0/opam
+++ b/packages/zeit/zeit.0.1.0/opam
@@ -16,6 +16,9 @@ depends: [
   "ppx_deriving_yojson"
   "ppx_let" {< "v0.15"}
 ]
+conflicts: [
+  "cohttp-lwt-unix" {with-test & >= "5.0.0"}
+]
 build: [
   ["dune" "subst"] {dev}
   ["dune" "build" "-p" name "-j" jobs]