diff --git a/packages/charrua-core/charrua-core.0.10/opam b/packages/charrua-core/charrua-core.0.10/opam
index 59c49ae7468..7c9486be4a3 100644
--- a/packages/charrua-core/charrua-core.0.10/opam
+++ b/packages/charrua-core/charrua-core.0.10/opam
@@ -20,7 +20,7 @@ depends: [
   "ppx_sexp_conv" {build & < "v0.13"}
   "ppx_cstruct" {build}
   "menhir" {build}
-  "cstruct" {>= "3.0.1"}
+  "cstruct" {>= "3.0.1" & < "4.0.0"}
   "sexplib" {< "v0.13"}
   "ipaddr" {>= "2.5.0" & < "3.0.0"}
   "tcpip" {>= "3.2.0" & < "3.6.0"}
diff --git a/packages/charrua-core/charrua-core.0.11.0/opam b/packages/charrua-core/charrua-core.0.11.0/opam
index 99ac3710e39..0f234a5c992 100644
--- a/packages/charrua-core/charrua-core.0.11.0/opam
+++ b/packages/charrua-core/charrua-core.0.11.0/opam
@@ -14,18 +14,18 @@ build: [
 ]
 
 depends: [
-  "jbuilder" {build & >="1.0+beta7"}
+  "jbuilder" {build & >= "1.0+beta7"}
   "ppx_sexp_conv" {build & < "v0.13"}
-  "ppx_cstruct"   {build}
-  "menhir"        {build}
-  "ocaml"         {>= "4.0.3"}
-  "cstruct"       {>= "3.0.1"}
-  "sexplib"       {< "v0.13"}
-  "ipaddr"        {>= "2.5.0" & < "3.0.0"}
-  "tcpip"         {>= "3.2.0" & < "3.6.0"}
+  "ppx_cstruct" {build}
+  "menhir" {build}
+  "ocaml" {>= "4.0.3"}
+  "cstruct" {>= "3.0.1" & < "4.0.0"}
+  "sexplib" {< "v0.13"}
+  "ipaddr" {>= "2.5.0" & < "3.0.0"}
+  "tcpip" {>= "3.2.0" & < "3.6.0"}
   "rresult"
-  "io-page-unix"  {with-test}
-  "cstruct-unix"  {with-test}
+  "io-page-unix" {with-test}
+  "cstruct-unix" {with-test}
 ]
 synopsis: "DHCP wire frame encoder and decoder"
 description: """
@@ -58,4 +58,4 @@ southern South America.
 url {
 archive: "https://github.com/mirage/charrua-core/releases/download/v0.11.0/charrua-core-0.11.0.tbz"
 checksum: "f4bb1ac3d1443a576982eae49d0eb7d8"
-}
\ No newline at end of file
+}
diff --git a/packages/charrua-core/charrua-core.0.11.1/opam b/packages/charrua-core/charrua-core.0.11.1/opam
index 5d75517082e..38a8c224bfb 100644
--- a/packages/charrua-core/charrua-core.0.11.1/opam
+++ b/packages/charrua-core/charrua-core.0.11.1/opam
@@ -14,19 +14,19 @@ build: [
 ]
 
 depends: [
-  "jbuilder" {build & >="1.0+beta7"}
+  "jbuilder" {build & >= "1.0+beta7"}
   "ppx_sexp_conv" {build & < "v0.13"}
-  "ppx_cstruct"   {build}
-  "menhir"        {build}
-  "ocaml"         {>= "4.0.3"}
-  "cstruct"       {>= "3.0.1"}
-  "sexplib"       {< "v0.13"}
-  "ipaddr"        {>= "3.0.0"}
+  "ppx_cstruct" {build}
+  "menhir" {build}
+  "ocaml" {>= "4.0.3"}
+  "cstruct" {>= "3.0.1" & < "4.0.0"}
+  "sexplib" {< "v0.13"}
+  "ipaddr" {>= "3.0.0"}
   "macaddr"
-  "tcpip"         {>= "3.6.0" & <"3.7.0"}
+  "tcpip" {>= "3.6.0" & < "3.7.0"}
   "rresult"
-  "io-page-unix"  {with-test}
-  "cstruct-unix"  {with-test}
+  "io-page-unix" {with-test}
+  "cstruct-unix" {with-test}
 ]
 synopsis: "DHCP wire frame encoder and decoder"
 description: """
diff --git a/packages/charrua-core/charrua-core.0.11.2/opam b/packages/charrua-core/charrua-core.0.11.2/opam
index aaa3b1a8b76..14838241f8c 100644
--- a/packages/charrua-core/charrua-core.0.11.2/opam
+++ b/packages/charrua-core/charrua-core.0.11.2/opam
@@ -19,7 +19,7 @@ depends: [
   "ppx_cstruct"
   "menhir" {build}
   "ocaml" {>= "4.0.3"}
-  "cstruct" {>= "3.0.1"}
+  "cstruct" {>= "3.0.1" & < "4.0.0"}
   "sexplib" {< "v0.13"}
   "ipaddr" {>= "3.0.0"}
   "macaddr"
diff --git a/packages/charrua-core/charrua-core.0.12.0/opam b/packages/charrua-core/charrua-core.0.12.0/opam
index 0a4266833b5..06b59af689a 100644
--- a/packages/charrua-core/charrua-core.0.12.0/opam
+++ b/packages/charrua-core/charrua-core.0.12.0/opam
@@ -17,16 +17,16 @@ depends: [
   "dune" {build & >= "1.0"}
   "ppx_sexp_conv" {< "v0.13"}
   "ppx_cstruct"
-  "menhir"        {build}
-  "ocaml"         {>= "4.0.3"}
-  "cstruct"       {>= "3.0.1"}
-  "sexplib"       {< "v0.13"}
-  "ipaddr"        {>= "3.0.0"}
+  "menhir" {build}
+  "ocaml" {>= "4.0.3"}
+  "cstruct" {>= "3.0.1" & < "4.0.0"}
+  "sexplib" {< "v0.13"}
+  "ipaddr" {>= "3.0.0"}
   "macaddr"
   "ethernet"
-  "tcpip"         {>= "3.7.0"}
+  "tcpip" {>= "3.7.0"}
   "rresult"
-  "cstruct-unix"  {with-test}
+  "cstruct-unix" {with-test}
 ]
 synopsis: "DHCP wire frame encoder and decoder"
 description: """
diff --git a/packages/charrua-core/charrua-core.0.8/opam b/packages/charrua-core/charrua-core.0.8/opam
index 25789cdc2de..86d5b4d9d7b 100644
--- a/packages/charrua-core/charrua-core.0.8/opam
+++ b/packages/charrua-core/charrua-core.0.8/opam
@@ -20,7 +20,7 @@ depends: [
   "ppx_sexp_conv" {< "v0.13"}
   "ppx_cstruct"
   "menhir" {build}
-  "cstruct" {>= "3.0.1"}
+  "cstruct" {>= "3.0.1" & < "4.0.0"}
   "sexplib" {< "v0.13"}
   "ipaddr" {>= "2.5.0" & < "3.0.0"}
   "tcpip" {>= "3.1.0" & < "3.2.0"}
diff --git a/packages/charrua-core/charrua-core.0.9/opam b/packages/charrua-core/charrua-core.0.9/opam
index 5307d855ebe..7f11032da2c 100644
--- a/packages/charrua-core/charrua-core.0.9/opam
+++ b/packages/charrua-core/charrua-core.0.9/opam
@@ -20,7 +20,7 @@ depends: [
   "ppx_sexp_conv" {< "v0.13"}
   "ppx_cstruct"
   "menhir" {build}
-  "cstruct" {>= "3.0.1"}
+  "cstruct" {>= "3.0.1" & < "4.0.0"}
   "sexplib" {< "v0.13"}
   "ipaddr" {>= "2.5.0" & < "3.0.0"}
   "tcpip" {>= "3.2.0" & < "3.6.0"}
diff --git a/packages/protocol-9p/protocol-9p.0.1/opam b/packages/protocol-9p/protocol-9p.0.1/opam
index 66c47dd7ff4..88fc71ac276 100644
--- a/packages/protocol-9p/protocol-9p.0.1/opam
+++ b/packages/protocol-9p/protocol-9p.0.1/opam
@@ -18,7 +18,7 @@ remove: [
 depends: [
   "ocaml" {>= "4.02.0"}
   "result"
-  "cstruct"
+  "cstruct" {< "4.0.0"}
   "sexplib" {< "113.01.00"}
   "cmdliner"
   "mirage-types-lwt" {< "3.0.0"}
diff --git a/packages/protocol-9p/protocol-9p.0.10.0/opam b/packages/protocol-9p/protocol-9p.0.10.0/opam
index faa8c5d8197..792e0d5ba09 100644
--- a/packages/protocol-9p/protocol-9p.0.10.0/opam
+++ b/packages/protocol-9p/protocol-9p.0.10.0/opam
@@ -14,7 +14,7 @@ build: [
 depends: [
   "ocaml" {>= "4.03.0"}
   "base-bytes"
-  "cstruct" {>= "1.9.0"}
+  "cstruct" {>= "1.9.0" & < "4.0.0"}
   "cstruct-lwt" {< "3.4.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "result"
diff --git a/packages/protocol-9p/protocol-9p.0.11.0/opam b/packages/protocol-9p/protocol-9p.0.11.0/opam
index 475e6465c3c..1a25cbf17c7 100644
--- a/packages/protocol-9p/protocol-9p.0.11.0/opam
+++ b/packages/protocol-9p/protocol-9p.0.11.0/opam
@@ -20,7 +20,7 @@ depends: [
   "ppx_tools"
   "ppx_cstruct" {< "3.4.0"}
   "base-bytes"
-  "cstruct" {>= "1.9.0"}
+  "cstruct" {>= "1.9.0" & < "4.0.0"}
   "cstruct-lwt" {< "3.4.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "result"
diff --git a/packages/protocol-9p/protocol-9p.0.11.1/opam b/packages/protocol-9p/protocol-9p.0.11.1/opam
index 6cf4bc91452..ab19ac73770 100644
--- a/packages/protocol-9p/protocol-9p.0.11.1/opam
+++ b/packages/protocol-9p/protocol-9p.0.11.1/opam
@@ -19,7 +19,7 @@ depends: [
   "ppx_tools"
   "ppx_cstruct" {< "3.4.0"}
   "base-bytes"
-  "cstruct" {>= "1.9.0"}
+  "cstruct" {>= "1.9.0" & < "4.0.0"}
   "cstruct-lwt" {< "3.4.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "result"
diff --git a/packages/protocol-9p/protocol-9p.0.11.2/opam b/packages/protocol-9p/protocol-9p.0.11.2/opam
index 73472beb0c4..23d1c0e897a 100644
--- a/packages/protocol-9p/protocol-9p.0.11.2/opam
+++ b/packages/protocol-9p/protocol-9p.0.11.2/opam
@@ -15,7 +15,7 @@ depends: [
   "ocaml" {>= "4.03.0"}
   "jbuilder" {build & >= "1.0+beta10"}
   "base-bytes"
-  "cstruct" {>= "3.0.0"}
+  "cstruct" {>= "3.0.0" & < "4.0.0"}
   "cstruct-lwt" {>= "3.0.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "result"
diff --git a/packages/protocol-9p/protocol-9p.0.11.3/opam b/packages/protocol-9p/protocol-9p.0.11.3/opam
index 132f54d9daf..79de2f81209 100644
--- a/packages/protocol-9p/protocol-9p.0.11.3/opam
+++ b/packages/protocol-9p/protocol-9p.0.11.3/opam
@@ -15,7 +15,7 @@ depends: [
   "ocaml" {>= "4.03.0"}
   "jbuilder" {build & >= "1.0+beta10"}
   "base-bytes"
-  "cstruct" {>= "3.0.0"}
+  "cstruct" {>= "3.0.0" & < "4.0.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "result"
   "rresult"
diff --git a/packages/protocol-9p/protocol-9p.0.12.0/opam b/packages/protocol-9p/protocol-9p.0.12.0/opam
index 24e75ed3e48..fa821b6f0f9 100644
--- a/packages/protocol-9p/protocol-9p.0.12.0/opam
+++ b/packages/protocol-9p/protocol-9p.0.12.0/opam
@@ -15,7 +15,7 @@ depends: [
   "ocaml" {>= "4.03.0"}
   "jbuilder" {build & >= "1.0+beta10"}
   "base-bytes"
-  "cstruct" {>= "3.0.0"}
+  "cstruct" {>= "3.0.0" & < "4.0.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "result"
   "rresult"
diff --git a/packages/protocol-9p/protocol-9p.0.12.1/opam b/packages/protocol-9p/protocol-9p.0.12.1/opam
index 1138b8da84f..4df7afbbefc 100644
--- a/packages/protocol-9p/protocol-9p.0.12.1/opam
+++ b/packages/protocol-9p/protocol-9p.0.12.1/opam
@@ -15,7 +15,7 @@ depends: [
   "ocaml" {>= "4.03.0"}
   "jbuilder" {build & >= "1.0+beta10"}
   "base-bytes"
-  "cstruct" {>= "3.0.0"}
+  "cstruct" {>= "3.0.0" & < "4.0.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "result"
   "rresult"
diff --git a/packages/protocol-9p/protocol-9p.0.2/opam b/packages/protocol-9p/protocol-9p.0.2/opam
index ec7fdedca3a..5c314feea50 100644
--- a/packages/protocol-9p/protocol-9p.0.2/opam
+++ b/packages/protocol-9p/protocol-9p.0.2/opam
@@ -18,7 +18,7 @@ remove: [
 depends: [
   "ocaml" {>= "4.02.0"}
   "result"
-  "cstruct"
+  "cstruct" {< "4.0.0"}
   "sexplib" {< "113.01.00"}
   "cmdliner"
   "mirage-types-lwt" {< "3.0.0"}
diff --git a/packages/protocol-9p/protocol-9p.0.3/opam b/packages/protocol-9p/protocol-9p.0.3/opam
index 2d46951fe49..622badf1b4a 100644
--- a/packages/protocol-9p/protocol-9p.0.3/opam
+++ b/packages/protocol-9p/protocol-9p.0.3/opam
@@ -21,7 +21,7 @@ remove: [
 depends: [
   "ocaml" {>= "4.02.0"}
   "base-bytes"
-  "cstruct"
+  "cstruct" {< "4.0.0"}
   "sexplib" {<= "113.00.00"}
   "result"
   "mirage-types-lwt" {< "3.0.0"}
diff --git a/packages/protocol-9p/protocol-9p.0.4.0/opam b/packages/protocol-9p/protocol-9p.0.4.0/opam
index def3c2596a3..f20589d32f3 100644
--- a/packages/protocol-9p/protocol-9p.0.4.0/opam
+++ b/packages/protocol-9p/protocol-9p.0.4.0/opam
@@ -16,7 +16,7 @@ remove: ["ocamlfind" "remove" "protocol-9p"]
 depends: [
   "ocaml" {>= "4.02.0"}
   "base-bytes"
-  "cstruct"
+  "cstruct" {< "4.0.0"}
   "sexplib" {<= "113.00.00"}
   "result"
   "mirage-types-lwt" {< "3.0.0"}
diff --git a/packages/protocol-9p/protocol-9p.0.5.0/opam b/packages/protocol-9p/protocol-9p.0.5.0/opam
index 16404103616..3b4a42681da 100644
--- a/packages/protocol-9p/protocol-9p.0.5.0/opam
+++ b/packages/protocol-9p/protocol-9p.0.5.0/opam
@@ -16,7 +16,7 @@ remove: ["ocamlfind" "remove" "protocol-9p"]
 depends: [
   "ocaml" {>= "4.02.0"}
   "base-bytes"
-  "cstruct"
+  "cstruct" {< "4.0.0"}
   "sexplib" {<= "113.00.00"}
   "result"
   "mirage-types-lwt" {< "3.0.0"}
diff --git a/packages/protocol-9p/protocol-9p.1.0.0/opam b/packages/protocol-9p/protocol-9p.1.0.0/opam
index b40a7d7d218..be212030747 100644
--- a/packages/protocol-9p/protocol-9p.1.0.0/opam
+++ b/packages/protocol-9p/protocol-9p.1.0.0/opam
@@ -9,7 +9,7 @@ depends: [
   "ocaml" {>= "4.03.0"}
   "dune" {build & >= "1.0"}
   "base-bytes"
-  "cstruct" {>= "3.0.0"}
+  "cstruct" {>= "3.0.0" & < "4.0.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "rresult"
   "mirage-flow-lwt"
diff --git a/packages/protocol-9p/protocol-9p.1.0.1/opam b/packages/protocol-9p/protocol-9p.1.0.1/opam
index cab7375c22a..9eb457c51f4 100644
--- a/packages/protocol-9p/protocol-9p.1.0.1/opam
+++ b/packages/protocol-9p/protocol-9p.1.0.1/opam
@@ -9,7 +9,7 @@ depends: [
   "ocaml" {>= "4.03.0"}
   "dune" {build & >= "1.0"}
   "base-bytes"
-  "cstruct" {>= "3.0.0"}
+  "cstruct" {>= "3.0.0" & < "4.0.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "rresult"
   "mirage-flow-lwt"
diff --git a/packages/protocol-9p/protocol-9p.2.0.0/opam b/packages/protocol-9p/protocol-9p.2.0.0/opam
index ad7566b129b..06cf4059064 100644
--- a/packages/protocol-9p/protocol-9p.2.0.0/opam
+++ b/packages/protocol-9p/protocol-9p.2.0.0/opam
@@ -9,7 +9,7 @@ depends: [
   "ocaml" {>= "4.03.0"}
   "dune" {build & >= "1.0"}
   "base-bytes"
-  "cstruct" {>= "3.0.0"}
+  "cstruct" {>= "3.0.0" & < "4.0.0"}
   "sexplib" {> "113.00.00" & < "v0.13"}
   "rresult"
   "mirage-flow-lwt"