diff --git a/cstruct-async.opam b/cstruct-async.opam
index 340b953..3fc684f 100644
--- a/cstruct-async.opam
+++ b/cstruct-async.opam
@@ -15,7 +15,7 @@ build: [
 ]
 depends: [
   "ocaml" {>= "4.08.0"}
-  "dune" {>= "2.0.0"}
+  "dune" {>= "3.17"}
   "async" {>= "v0.9.0" & < "v0.17.0"}
   "async_unix" {>= "v0.9.0" & < "v0.17.0"}
   "core" {>= "v0.9.0" & < "v0.17.0"}
diff --git a/cstruct-lwt.opam b/cstruct-lwt.opam
index 4f702c7..dc5a955 100644
--- a/cstruct-lwt.opam
+++ b/cstruct-lwt.opam
@@ -16,7 +16,7 @@ build: [
 depends: [
   "ocaml" {>= "4.08.0"}
   "base-unix"
-  "dune" {>= "2.0.0"}
+  "dune" {>= "3.17"}
   "lwt"
   "cstruct" {=version}
 ]
diff --git a/cstruct-sexp.opam b/cstruct-sexp.opam
index 6181a9c..c9f6d85 100644
--- a/cstruct-sexp.opam
+++ b/cstruct-sexp.opam
@@ -17,7 +17,7 @@ build: [
 ]
 depends: [
   "ocaml" {>= "4.08.0"}
-  "dune" {>= "2.0.0"}
+  "dune" {>= "3.17"}
   "sexplib"
   "cstruct" {=version}
   "alcotest" {with-test}
diff --git a/cstruct-unix.opam b/cstruct-unix.opam
index 0cda0a0..f6e099f 100644
--- a/cstruct-unix.opam
+++ b/cstruct-unix.opam
@@ -16,7 +16,7 @@ build: [
 ]
 depends: [
   "ocaml" {>= "4.06.0"}
-  "dune" {>= "2.0.0"}
+  "dune" {>= "3.17"}
   "base-unix"
   "cstruct" {=version}
 ]
diff --git a/cstruct.opam b/cstruct.opam
index 6830762..faa7d6d 100644
--- a/cstruct.opam
+++ b/cstruct.opam
@@ -17,7 +17,7 @@ build: [
 ]
 depends: [
   "ocaml" {>= "4.08.0"}
-  "dune" {>= "2.0.0"}
+  "dune" {>= "3.17"}
   "alcotest" {with-test}
   "fmt" {>= "0.8.9"}
   "crowbar" {with-test & >= "0.2"}
diff --git a/dune-project b/dune-project
index 9517716..5c627f8 100644
--- a/dune-project
+++ b/dune-project
@@ -1,5 +1,3 @@
-(lang dune 2.0)
-
-(allow_approximate_merlin)
+(lang dune 3.17)
 
 (name cstruct)
diff --git a/fuzz/fuzz.ml b/fuzz/fuzz.ml
index 75d2cfd..f50a5bd 100644
--- a/fuzz/fuzz.ml
+++ b/fuzz/fuzz.ml
@@ -25,8 +25,6 @@ let bytes = map [bytes] Bytes.unsafe_of_string
 
 let buffer = map [uint8] Bigarray.(Array1.create Char c_layout)
 
-let pp_cstruct f c = Format.pp_print_string f (Cstruct.debug c)
-
 let check_within ~base x =
   check Cstruct.(base.off <= x.off);
   check Cstruct.(base.off + base.len >= x.off + x.len);
diff --git a/ppx_cstruct.opam b/ppx_cstruct.opam
index 0c647ff..3a2289a 100644
--- a/ppx_cstruct.opam
+++ b/ppx_cstruct.opam
@@ -17,7 +17,7 @@ build: [
 ]
 depends: [
   "ocaml" {>= "4.08.0"}
-  "dune" {>= "2.0.0"}
+  "dune" {>= "3.17"}
   "cstruct" {=version}
   "ounit" {with-test}
   "ppxlib" {>= "0.16.0"}
diff --git a/ppx_test/with-lwt/ppx_cstruct_and_lwt.ml b/ppx_test/with-lwt/ppx_cstruct_and_lwt.ml
index 8fbd3b8..1a6455e 100644
--- a/ppx_test/with-lwt/ppx_cstruct_and_lwt.ml
+++ b/ppx_test/with-lwt/ppx_cstruct_and_lwt.ml
@@ -13,3 +13,5 @@ type foo64 =
 let foo = 
   let%lwt foo = Lwt.return () in 
   Lwt.return foo
+
+let () = ignore foo