diff --git a/pkgs/development/ocaml-modules/capnp/default.nix b/pkgs/development/ocaml-modules/capnp/default.nix
new file mode 100644
index 000000000000..2d405dceaab1
--- /dev/null
+++ b/pkgs/development/ocaml-modules/capnp/default.nix
@@ -0,0 +1,56 @@
+{ lib
+, buildDunePackage
+, fetchFromGitHub
+, base_quickcheck ? null
+, capnproto
+, ocplib-endian
+, ounit2
+, res
+, result
+, stdint
+, stdio
+}:
+
+buildDunePackage rec {
+  pname = "capnp";
+  version = "3.6.0";
+
+  minimalOCamlVersion = "4.08";
+
+  src = fetchFromGitHub {
+    owner = "capnproto";
+    repo = "capnp-ocaml";
+    rev = "v${version}";
+    hash = "sha256-G4B1llsHnGcuGIarDB248QMaRBvS47IEQB5B93wY7nA=";
+  };
+
+  nativeBuildInputs = [
+    capnproto
+  ];
+
+  buildInputs = [
+    stdio
+  ];
+
+  propagatedBuildInputs = [
+    ocplib-endian
+    res
+    result
+    stdint
+  ];
+
+  checkInputs = [
+    base_quickcheck
+    ounit2
+  ];
+
+  doCheck = true;
+
+  meta = {
+    description = "OCaml code generation plugin for the Cap'n Proto serialization framework";
+    homepage = "https://github.com/capnproto/capnp-ocaml";
+    changelog = "https://github.com/capnproto/capnp-ocaml/blob/${version}/CHANGES.md";
+    license = lib.licenses.bsd2;
+    maintainers = with lib.maintainers; [ sixstring982 ];
+  };
+}
diff --git a/pkgs/top-level/ocaml-packages.nix b/pkgs/top-level/ocaml-packages.nix
index 0dfdbdfc8c0a..5e59435d789b 100644
--- a/pkgs/top-level/ocaml-packages.nix
+++ b/pkgs/top-level/ocaml-packages.nix
@@ -156,6 +156,8 @@ let
       then callPackage ../development/ocaml-modules/camomile { }
       else callPackage ../development/ocaml-modules/camomile/0.8.5.nix { };
 
+    capnp = callPackage ../development/ocaml-modules/capnp { };
+
     caqti = callPackage ../development/ocaml-modules/caqti { };
 
     caqti-async = callPackage ../development/ocaml-modules/caqti/async.nix { };