diff --git a/benchmarks/benchmark.ml b/benchmarks/benchmark.ml
index 039c561..b75e4c2 100644
--- a/benchmarks/benchmark.ml
+++ b/benchmarks/benchmark.ml
@@ -166,5 +166,6 @@ let () =
            Printf.printf "- %s\n" name);
          exit 1)
   in
+  Memtrace.trace_if_requested ();
   Command_unix.run (Bench.make_command benchmarks)
 ;;
diff --git a/benchmarks/dune b/benchmarks/dune
index ab16c7b..50d43fe 100644
--- a/benchmarks/dune
+++ b/benchmarks/dune
@@ -4,5 +4,13 @@
    (:standard -w -58))))
 
 (executables
- (libraries re core base stdio threads core_bench core_unix.command_unix)
+ (libraries
+  re
+  core
+  base
+  stdio
+  threads
+  core_bench
+  core_unix.command_unix
+  memtrace)
  (names benchmark))
diff --git a/benchmarks/memory.ml b/benchmarks/memory.ml
index 0676e39..3adc6ca 100644
--- a/benchmarks/memory.ml
+++ b/benchmarks/memory.ml
@@ -29,3 +29,5 @@ let benchmarks =
         let len = Int.min (String.length str) len in
         ignore (Re.execp ~pos:0 ~len re str))))
 ;;
+
+let () = Command_unix.run (Bench.make_command benchmarks)
diff --git a/flake.nix b/flake.nix
index 3b15bdd..a3a05fd 100644
--- a/flake.nix
+++ b/flake.nix
@@ -7,23 +7,26 @@
   outputs = { self, nixpkgs, flake-utils }:
     flake-utils.lib.eachDefaultSystem (system:
       let
-        pkgs = nixpkgs.legacyPackages."${system}";
-        extraBuildInputs = [ pkgs.ocamlPackages.core_bench ];
-        checkInputs = with pkgs.ocamlPackages; [
-          ounit
-          js_of_ocaml
-          ppx_expect
-          pkgs.nodejs-slim
-        ];
-        devInputs = with pkgs.ocamlPackages; [
-          ocaml-lsp
-          pkgs.ocamlformat_0_26_2
-        ];
-        inherit (pkgs.ocamlPackages) buildDunePackage;
-      in rec {
-        packages = rec {
+        extraBuildInputs = pkgs:
+          with pkgs.ocamlPackages; [
+            core_bench
+            memtrace
+          ];
+        checkInputs = pkgs:
+          with pkgs.ocamlPackages; [
+            ounit
+            js_of_ocaml
+            ppx_expect
+            pkgs.nodejs-slim
+          ];
+        devInputs = pkgs:
+          with pkgs.ocamlPackages; [
+            ocaml-lsp
+            pkgs.ocamlformat_0_26_2
+          ];
+        makePackages = pkgs: rec {
           default = re;
-          re = buildDunePackage {
+          re = pkgs.ocamlPackages.buildDunePackage {
             pname = "re";
             version = "n/a";
             src = ./.;
@@ -34,13 +37,33 @@
             doCheck = true;
           };
         };
-        devShells.test = pkgs.mkShell {
+        ocamlVersionOverlay =
+          (ocaml: self: super: { ocamlPackages = ocaml super.ocaml-ng; });
+        makeNixpkgs = ocaml:
+        nixpkgs.legacyPackages.${system}.appendOverlays [ (ocamlVersionOverlay ocaml) ];
+      in rec {
+        # packages = makePackages pkgs;
+        devShells.test = let
+          pkgs = makeNixpkgs (ocaml: ocaml.ocamlPackages_5_2);
+          packages = makePackages pkgs;
+        in pkgs.mkShell {
+          inputsFrom = pkgs.lib.attrValues packages;
+          buildInputs = extraBuildInputs pkgs ++ checkInputs pkgs;
+        };
+        devShells.default = let
+          pkgs = makeNixpkgs (ocaml: ocaml.ocamlPackages_5_2);
+          packages = makePackages pkgs;
+        in pkgs.mkShell {
           inputsFrom = pkgs.lib.attrValues packages;
-          buildInputs = extraBuildInputs ++ checkInputs;
+          buildInputs = extraBuildInputs pkgs ++ devInputs pkgs;
         };
-        devShells.default = pkgs.mkShell {
+        devShells.memtrace = let
+          pkgs = makeNixpkgs (ocaml: ocaml.ocamlPackages_4_14);
+          packages = makePackages pkgs;
+        in pkgs.mkShell {
           inputsFrom = pkgs.lib.attrValues packages;
-          buildInputs = extraBuildInputs ++ devInputs;
+          buildInputs = extraBuildInputs pkgs
+            ++ [ pkgs.ocamlPackages.memtrace_viewer ];
         };
       });
 }