diff --git a/.github/workflows/nix-build.yml b/.github/workflows/nix-build.yml
index 48b4d027a..e60fea190 100644
--- a/.github/workflows/nix-build.yml
+++ b/.github/workflows/nix-build.yml
@@ -11,54 +11,25 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  ubuntu-tests:
+  nix-build-test:
     name: Build and test (Ubuntu)
 
-    strategy:
-      matrix:
-        ocaml-version:
-          - 5_3
-
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          submodules: "recursive"
-      - uses: cachix/install-nix-action@v30
-        with:
-          extra_nix_config: |
-            extra-substituters = https://anmonteiro.nix-cache.workers.dev
-            extra-trusted-public-keys = ocaml.nix-cache.com-1:/xI2h2+56rwFfKyyFVbkJSeGqSIYMC/Je+7XXqGKDIY=
-
-      - name: "Build / install dependencies"
-        run: nix-shell ./nix/ci/prewarm.nix --argstr ocamlVersion ${{ matrix.ocaml-version }} --run 'echo done'
-      - name: "Run nix-build"
-        run: nix-build ./nix/ci/test.nix --argstr ocamlVersion ${{ matrix.ocaml-version }}
-
-  macos-tests:
-    name: Build and test (${{ matrix.os }})
-
     strategy:
       matrix:
         os:
+          - ubuntu-latest
           - macos-13
           - macos-14
-        ocaml-version:
-          - 5_3
 
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
         with:
           submodules: "recursive"
-
       - uses: cachix/install-nix-action@v30
         with:
           extra_nix_config: |
             extra-substituters = https://anmonteiro.nix-cache.workers.dev
             extra-trusted-public-keys = ocaml.nix-cache.com-1:/xI2h2+56rwFfKyyFVbkJSeGqSIYMC/Je+7XXqGKDIY=
-
-      # - name: "Build / install dependencies"
-        # run: nix-shell ./nix/ci/prewarm.nix --argstr ocamlVersion ${{ matrix.ocaml-version }} --run 'echo done'
       - name: "Run nix-build"
-        run: nix-build ./nix/ci/test.nix --argstr ocamlVersion ${{ matrix.ocaml-version }}
+        run: nix flake check
diff --git a/flake.nix b/flake.nix
index 21f20c545..facc1ac9c 100644
--- a/flake.nix
+++ b/flake.nix
@@ -61,5 +61,18 @@
           };
         }
       );
+
+      checks = nixpkgs.lib.genAttrs nixpkgs.lib.systems.flakeExposed (system:
+        let
+          pkgs = nixpkgs.legacyPackages.${system}.extend (self: super: {
+            ocamlPackages = super.ocaml-ng.ocamlPackages_5_3;
+          });
+        in
+        {
+          melange-check = pkgs.callPackage ./nix/ci/test.nix {
+            packages = self.packages.${pkgs.system};
+          };
+        }
+      );
     };
 }
diff --git a/nix/ci/prewarm.nix b/nix/ci/prewarm.nix
deleted file mode 100644
index e225b4c31..000000000
--- a/nix/ci/prewarm.nix
+++ /dev/null
@@ -1,7 +0,0 @@
-{ ocamlVersion }:
-
-let
-  src = import ./sources.nix { inherit ocamlVersion; };
-  inherit (src) pkgs packages;
-in
-packages.melange
diff --git a/nix/ci/sources.nix b/nix/ci/sources.nix
deleted file mode 100644
index dfc8e83c6..000000000
--- a/nix/ci/sources.nix
+++ /dev/null
@@ -1,33 +0,0 @@
-{ ocamlVersion }:
-
-let
-  lock = builtins.fromJSON (builtins.readFile ./../../flake.lock);
-  findFlakeSrc = { name, allRefs ? false }: fetchGit {
-    url = with lock.nodes.${name}.locked;"https://github.com/${owner}/${repo}";
-    inherit (lock.nodes.${name}.locked) rev;
-    inherit allRefs;
-  };
-
-  src = findFlakeSrc { name = "nixpkgs"; };
-  nix-filter-src = findFlakeSrc { name = "nix-filter"; };
-  melange-compiler-libs-src = findFlakeSrc {
-    name = "melange-compiler-libs";
-    allRefs = true;
-  };
-  nix-filter = import "${nix-filter-src}";
-
-  pkgs = import src {
-    extraOverlays = [
-      (self: super: {
-        ocamlPackages = super.ocaml-ng."ocamlPackages_${ocamlVersion}";
-      })
-    ];
-  };
-  packages = rec {
-    melange = pkgs.callPackage ./.. {
-      inherit nix-filter;
-      melange-compiler-libs-vendor-dir = melange-compiler-libs-src;
-    };
-  };
-in
-{ inherit pkgs packages; }
diff --git a/nix/ci/test.nix b/nix/ci/test.nix
index dd7b8574d..fe49cb1be 100644
--- a/nix/ci/test.nix
+++ b/nix/ci/test.nix
@@ -1,8 +1,6 @@
-{ ocamlVersion }:
+{ pkgs, packages }:
 
 let
-  src = import ./sources.nix { inherit ocamlVersion; };
-  inherit (src) pkgs packages;
   inputString =
     builtins.substring
       11 32
@@ -31,7 +29,7 @@ stdenv.mkDerivation {
     dune
     git
     nodePackages.mocha
-    ocamlPackages.reason
+    reason
     tree
     nodejs
     yarn