diff --git a/.github/run-ghcjs-tests.sh b/.github/run-ghcjs-tests.sh
new file mode 100755
index 00000000..19e0d9b7
--- /dev/null
+++ b/.github/run-ghcjs-tests.sh
@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+#
+# cabal v2-test does not work with GHCJS
+# See: https://github.com/haskell/cabal/issues/6175
+#
+# This invokes cabal-plan to figure out test binaries, and invokes them with node.
+
+cabal-plan list-bins '*:test:*' | while read -r line
+do
+    testpkg=$(echo "$line" | perl -pe 's/:.*//')
+    testexe=$(echo "$line" | awk '{ print $2 }')
+    echo "testing $textexe in package $textpkg"
+    (cd "$testpkg" && node "$testexe".jsexe/all.js)
+done
diff --git a/.github/workflows/master.yml b/.github/workflows/master.yml
index 2eea692c..642b4e30 100644
--- a/.github/workflows/master.yml
+++ b/.github/workflows/master.yml
@@ -172,8 +172,40 @@ jobs:
 
     - name: Run tests
       run: |
-        # cabal v2-test does not work with GHCJS
-        # See: https://github.com/haskell/cabal/issues/6175
-        #
-        # This invokes cabal-plan to figure out test binaries, and invokes them with node.
         cabal-plan list-bins '*:test:*' | while read -r line; do testpkg=$(echo "$line" | perl -pe 's/:.*//'); testexe=$(echo "$line" | awk '{ print $2 }'); echo "testing $textexe in package $textpkg"; (cd "$(pkgdir $testpkg)" && nodejs "$testexe".jsexe/all.js); done
+
+  ghcjs-test:
+    name: ghcjs-test
+    runs-on: "ubuntu-latest"
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: cachix/install-nix-action@v13
+      with:
+        extra_nix_config: |
+          trusted-public-keys = ryantrinkle.com-1:JJiAKaRv9mWgpVAz8dwewnZe0AzzEAzPkagE9SP5NWI=1aba6f367982bd6dd78ec2fda75ab246a62d32c5 cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+          substituters = https://nixcache.reflex-frp.org https://cache.nixos.org/
+    - name: Setup
+      run: |
+        # Override cabal.project with the lightweight GHCJS one
+        cp cabal.ghcjs.project cabal.project
+        cat cabal.project
+        nix-shell ghcjs.nix --run "cabal v2-update && cabal v2-freeze"
+
+    - uses: actions/cache@v2.1.3
+      name: Cache ~/.cabal/store and dist-newstyle
+      with:
+        path: |
+          ~/.cabal/store
+          dist-newstyle
+        key: ${{ runner.os }}-ghcjs8.6-${{ hashFiles('cabal.project.freeze') }}
+        restore-keys: |
+          ${{ runner.os }}-ghcjs8.6-
+
+    - name: Build
+      run: |
+        nix-shell ghcjs.nix --run "cabal v2-build --ghcjs --enable-tests --enable-benchmarks all"
+
+    - name: Tests
+      run: |
+        nix-shell ghcjs.nix --run ".github/run-ghcjs-tests.sh"
diff --git a/cabal.ghcjs.project b/cabal.ghcjs.project
index 72902332..db1ef33a 100644
--- a/cabal.ghcjs.project
+++ b/cabal.ghcjs.project
@@ -8,4 +8,6 @@ packages:
 compiler: ghcjs
 tests: True
 
-constraints: hashable <=1.3.3.0
+-- Constraints so that reflex-platform provided packages are selected.
+constraints: attoparsec == 0.13.2.2
+constraints: hashable == 1.3.0.0
diff --git a/ghcjs.nix b/ghcjs.nix
new file mode 100644
index 00000000..274d007c
--- /dev/null
+++ b/ghcjs.nix
@@ -0,0 +1,22 @@
+let reflex-platform = import (builtins.fetchTarball
+      { name = "reflex-platform";
+        url = "https://github.com/reflex-frp/reflex-platform/archive/1aba6f367982bd6dd78ec2fda75ab246a62d32c5.tar.gz";
+      }) {};
+    pkgs = import ./nix/nixpkgs.nix; in
+
+pkgs.stdenv.mkDerivation {
+  name = "ghcjs-shell";
+  buildInputs =
+    [ (reflex-platform.ghcjs.ghcWithPackages (p: with p; [
+        attoparsec
+        hashable
+      ]))
+      pkgs.cabal-install
+      pkgs.gmp
+      pkgs.haskellPackages.cabal-plan
+      pkgs.haskellPackages.hspec-discover
+      pkgs.nodejs
+      pkgs.perl
+      pkgs.zlib
+    ];
+}
diff --git a/nix/nixpkgs.nix b/nix/nixpkgs.nix
new file mode 100644
index 00000000..744f982c
--- /dev/null
+++ b/nix/nixpkgs.nix
@@ -0,0 +1,4 @@
+import (builtins.fetchTarball {
+  url = "https://github.com/NixOS/nixpkgs/archive/refs/tags/21.05.tar.gz";
+  sha256 = "sha256:1ckzhh24mgz6jd1xhfgx0i9mijk6xjqxwsshnvq789xsavrmsc36";
+}) {}
diff --git a/nix/shell.nix b/nix/shell.nix
index 715004f6..d178b60e 100644
--- a/nix/shell.nix
+++ b/nix/shell.nix
@@ -1,10 +1,6 @@
-let nixos = fetchTarball { url = "https://github.com/NixOS/nixpkgs/archive/refs/tags/21.05.tar.gz"; 
-                           sha256 = "sha256:1ckzhh24mgz6jd1xhfgx0i9mijk6xjqxwsshnvq789xsavrmsc36";
-}; in
-
 { compiler ? "ghc8104"
 , tutorial ? false
-, pkgs ? import nixos { config = {}; }
+, pkgs ? import ./nixpkgs.nix
 }:
   
   with pkgs;