diff --git a/flake.lock b/flake.lock
index 30b5752c..9e049171 100644
--- a/flake.lock
+++ b/flake.lock
@@ -20,17 +20,17 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1727631725,
-        "narHash": "sha256-3BhOfmcg9Pxjm/kU+IVYe76CvHL6zArK9ktlCJeP06E=",
+        "lastModified": 1727696162,
+        "narHash": "sha256-ENlNwIXX6xrh2RQeJeyTRYIRHvwCQYZPAM34XgkmX0U=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "b5c4f45cfcaa5a44632c7119922987e131249cd2",
+        "rev": "16524a25426bd886b43dd41ebab1472a6a1a8fad",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "b5c4f45cfcaa5a44632c7119922987e131249cd2",
+        "rev": "16524a25426bd886b43dd41ebab1472a6a1a8fad",
         "type": "github"
       }
     },
diff --git a/flake.nix b/flake.nix
index 2ebb95c0..b6145a3c 100644
--- a/flake.nix
+++ b/flake.nix
@@ -7,7 +7,7 @@
   };
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs?rev=b5c4f45cfcaa5a44632c7119922987e131249cd2";
+    nixpkgs.url = "github:NixOS/nixpkgs?rev=16524a25426bd886b43dd41ebab1472a6a1a8fad";
     flake-utils.url = "github:numtide/flake-utils";
   };
 
diff --git a/ocaml/default.nix b/ocaml/default.nix
index 8d55c7db..5c6c5f75 100644
--- a/ocaml/default.nix
+++ b/ocaml/default.nix
@@ -890,6 +890,11 @@ with oself;
       '';
     });
 
+  eio-ssl =
+    if lib.versionAtLeast ocaml.version "5.0" then
+      callPackage ./eio-ssl { }
+    else null;
+
   extlib = osuper.extlib.overrideAttrs (_: {
     src = fetchFromGitHub {
       owner = "ygrek";
@@ -1028,6 +1033,11 @@ with oself;
   h2-lwt-unix = callPackage ./h2/lwt-unix.nix { };
   h2-mirage = callPackage ./h2/mirage.nix { };
   h2-async = callPackage ./h2/async.nix { };
+  h2-eio =
+    if lib.versionAtLeast ocaml.version "5.0" then
+      callPackage ./h2/eio.nix { }
+    else null;
+
   hpack = callPackage ./h2/hpack.nix { };
 
   hachis = buildDunePackage {
@@ -1089,6 +1099,10 @@ with oself;
   httpun-lwt-unix = callPackage ./httpun/lwt-unix.nix { };
   httpun-mirage = callPackage ./httpun/mirage.nix { };
   httpun-async = callPackage ./httpun/async.nix { };
+  httpun-eio =
+    if lib.versionAtLeast ocaml.version "5.0" then
+      callPackage ./httpun/eio.nix { }
+    else null;
 
   hxd = osuper.hxd.overrideAttrs (o: {
     buildInputs = o.buildInputs ++ [ dune-configurator ];
@@ -2085,6 +2099,11 @@ with oself;
 
   pg_query = callPackage ./pg_query { };
 
+  piaf =
+    if lib.versionAtLeast ocaml.version "5.0" then
+      callPackage ./piaf { }
+    else null;
+
   plist-xml = buildDunePackage {
     pname = "plist-xml";
     version = "";
diff --git a/ocaml/ocaml5.nix b/ocaml/ocaml5.nix
index ec3fadc0..1a662c42 100644
--- a/ocaml/ocaml5.nix
+++ b/ocaml/ocaml5.nix
@@ -26,8 +26,6 @@ with oself;
     propagatedBuildInputs = [ cohttp eio_main ptime ];
   };
 
-  eio-ssl = callPackage ./eio-ssl { };
-
   eio-trace =
     let
       stdenv' = if stdenv.isDarwin then overrideSDK stdenv "11.0" else stdenv;
@@ -52,10 +50,6 @@ with oself;
     propagatedBuildInputs = [ eio_main graphql ];
   };
 
-  h2-eio = callPackage ./h2/eio.nix { };
-
-  httpun-eio = callPackage ./httpun/eio.nix { };
-
   kafka-eio = buildDunePackage {
     pname = "kafka-eio";
     inherit (kafka) hardeningDisable version src;
@@ -92,7 +86,6 @@ with oself;
     checkInputs = [ mdx qcheck-core trace trace-tef ];
   };
 
-  piaf = callPackage ./piaf { };
   carl = callPackage ./piaf/carl.nix { };
 
   picos = buildDunePackage {