diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 9dc3eccc2..c6c3a7dc6 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -1,6 +1,6 @@
 # This is a basic workflow to help you get started with Actions
 
-name: CI
+name: docker CI
 
 # Controls when the action will run. Triggers the workflow on push or pull request
 # events but only for the master branch
@@ -11,19 +11,6 @@ on:
     branches: [ master ]
 
 jobs:
-  nix:
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/checkout@v2
-      with:
-        fetch-depth: 0
-    - uses: cachix/install-nix-action@v12
-    - uses: cachix/cachix-action@v8
-      with:
-        name: coq
-    - run: nix-build
-
   opam:
     runs-on: ubuntu-latest
     strategy:
diff --git a/.github/workflows/nix.yml b/.github/workflows/nix.yml
new file mode 100644
index 000000000..7b840d580
--- /dev/null
+++ b/.github/workflows/nix.yml
@@ -0,0 +1,43 @@
+# This is a basic workflow to help you get started with Actions
+
+name: nix CI
+
+# Controls when the action will run. Triggers the workflow on push or pull request
+# events but only for the master branch
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  nix:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - uses: cachix/install-nix-action@v12
+    - uses: cachix/cachix-action@v8
+      with:
+        name: math-comp
+        extraPullNames: coq
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - run: nix-build
+
+  nixci:
+    runs-on: ubuntu-latest
+    needs: nix
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - uses: cachix/install-nix-action@v12
+    - uses: cachix/cachix-action@v8
+      with:
+        name: math-comp
+        extraPullNames: coq
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - run: nix-build --arg ci true
diff --git a/.nix/config.nix b/.nix/config.nix
index eadab65be..535edc14c 100644
--- a/.nix/config.nix
+++ b/.nix/config.nix
@@ -6,5 +6,7 @@
   select = "coq-8.13";
   inputs."coq-8.13".coqPackages = {
     coq.override.version = "8.13";
+    mathcomp.override.version = "gares:hierarchy-builder";
+    mathcomp-single.ci = true;
   };
 }
diff --git a/.nix/coq-overlays/mathcomp-single/default.nix b/.nix/coq-overlays/mathcomp-single/default.nix
new file mode 100644
index 000000000..228f5f62d
--- /dev/null
+++ b/.nix/coq-overlays/mathcomp-single/default.nix
@@ -0,0 +1,7 @@
+{ mathcomp, coq-elpi, hierarchy-builder, version ? null }:
+(mathcomp.override {single = true;}).overrideAttrs (old: {
+  buildPhase = "make -j $(max_jobs) -C mathcomp ./algebra/ssralg.vo";
+  propagatedBuildInputs = old.propagatedBuildInputs ++
+                          [ coq-elpi hierarchy-builder ];
+  installPhase = "echo NO INSTALL";
+})