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/lib/cstruct.wat b/lib/cstruct.wat
new file mode 100644
index 0000000..2b30872
--- /dev/null
+++ b/lib/cstruct.wat
@@ -0,0 +1,39 @@
+;; The Wasm runtime for cstruct's bigstring primitives -- the analog of
+;; cstruct.js for wasm_of_ocaml. wasm_of_ocaml's runtime already provides these
+;; operations under its own bigarray names, so each cstruct primitive simply
+;; re-exports the matching runtime function; only caml_check_alignment_bigstring
+;; is cstruct-specific.
+(module
+   (import "env" "caml_bigstring_blit_ba_to_ba"
+      (func $caml_blit_bigstring_to_bigstring
+         (param (ref eq)) (param (ref eq)) (param (ref eq)) (param (ref eq))
+         (param (ref eq)) (result (ref eq))))
+   (import "env" "caml_bigstring_blit_ba_to_bytes"
+      (func $caml_blit_bigstring_to_string
+         (param (ref eq)) (param (ref eq)) (param (ref eq)) (param (ref eq))
+         (param (ref eq)) (result (ref eq))))
+   (import "env" "caml_bigstring_blit_string_to_ba"
+      (func $caml_blit_string_to_bigstring
+         (param (ref eq)) (param (ref eq)) (param (ref eq)) (param (ref eq))
+         (param (ref eq)) (result (ref eq))))
+   (import "env" "caml_bigstring_memset"
+      (func $caml_fill_bigstring
+         (param (ref eq)) (param (ref eq)) (param (ref eq)) (param (ref eq))
+         (result (ref eq))))
+   (import "env" "caml_bigstring_memcmp"
+      (func $caml_compare_bigstring
+         (param (ref eq)) (param (ref eq)) (param (ref eq)) (param (ref eq))
+         (param (ref eq)) (result (ref eq))))
+
+   (export "caml_blit_bigstring_to_bigstring"
+      (func $caml_blit_bigstring_to_bigstring))
+   (export "caml_blit_bigstring_to_string" (func $caml_blit_bigstring_to_string))
+   (export "caml_blit_string_to_bigstring" (func $caml_blit_string_to_bigstring))
+   (export "caml_fill_bigstring" (func $caml_fill_bigstring))
+   (export "caml_compare_bigstring" (func $caml_compare_bigstring))
+
+   ;; No fixed buffer address on Wasm, as in cstruct.js: always aligned.
+   (func (export "caml_check_alignment_bigstring")
+      (param (ref eq)) (param (ref eq)) (param (ref eq)) (result (ref eq))
+      (ref.i31 (i32.const 1)))
+)
diff --git a/lib/dune b/lib/dune
index c1fa1de..4afea93 100644
--- a/lib/dune
+++ b/lib/dune
@@ -7,6 +7,8 @@
  (wrapped false)
  (js_of_ocaml
   (javascript_files cstruct.js))
+ (wasm_of_ocaml
+  (wasm_files cstruct.wat))
  (modules cstruct cstruct_cap))
 
 (library
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