diff --git a/.github/workflows/nix-action-coq-master.yml b/.github/workflows/nix-action-coq-master.yml
index 932525614..08d8b3ab0 100644
--- a/.github/workflows/nix-action-coq-master.yml
+++ b/.github/workflows/nix-action-coq-master.yml
@@ -27,7 +27,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -75,7 +75,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -84,12 +84,16 @@ jobs:
         authToken: ${{ secrets.CACHIX_AUTH_TOKEN }}
         extraPullNames: coq, coq-community, math-comp
         name: coq-elpi
+    - name: No idea what this does
+      run: "NIXPKGS_ALLOW_UNFREE=1 nix-build --no-out-link \\\n   --argstr
+        bundle \"coq-master\" --argstr job \"coq-elpi\" \\\n   --dry-run 2> err > out || (touch fail; true)"
+    - name: Error reporting
+      run: cat err
+    - name: Failure check
+      run: "if [ -e fail ]; then exit 1; else exit 0; fi"
     - id: stepCheck
       name: Checking presence of CI target coq-elpi
-      run: "nb_dry_run=$(NIXPKGS_ALLOW_UNFREE=1 nix-build --no-out-link \\\n   --argstr
-        bundle \"coq-master\" --argstr job \"coq-elpi\" \\\n   --dry-run 2>&1 > /dev/null)\n
-        echo $nb_dry_run\necho status=$(echo $nb_dry_run | grep \"built:\" | sed \"\
-        s/.*/built/\") >> $GITHUB_OUTPUT\n"
+      run: "cat out >> $GITHUB_OUTPUT; (echo -n status=; cat out | grep \"built:\" | sed \"s/.*/built/\") >> $GITHUB_OUTPUT\n"
     - if: steps.stepCheck.outputs.status == 'built'
       name: 'Building/fetching previous CI target: coq'
       run: NIXPKGS_ALLOW_UNFREE=1 nix-build --no-out-link --argstr bundle "coq-master"
@@ -128,7 +132,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -191,7 +195,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -274,7 +278,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -342,7 +346,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -413,7 +417,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -478,7 +482,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -540,7 +544,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -619,7 +623,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -686,7 +690,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -755,7 +759,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -829,7 +833,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -890,7 +894,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -952,7 +956,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -1030,7 +1034,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -1092,7 +1096,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -1156,7 +1160,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -1225,7 +1229,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -1286,7 +1290,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
@@ -1365,7 +1369,7 @@ jobs:
         fetch-depth: 0
         ref: ${{ env.tested_commit }}
     - name: Cachix install
-      uses: cachix/install-nix-action@v27
+      uses: cachix/install-nix-action@v30
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: Cachix setup coq-elpi
diff --git a/.nix/ocaml-overlays/elpi/default.nix b/.nix/ocaml-overlays/elpi/default.nix
index a40d50715..2a4da79f4 100644
--- a/.nix/ocaml-overlays/elpi/default.nix
+++ b/.nix/ocaml-overlays/elpi/default.nix
@@ -1,18 +1,15 @@
 { lib
-, buildDunePackage, camlp5
+, buildDunePackage
 , ocaml
 , menhir, menhirLib
 , atdgen
 , stdlib-shims
-, re, perl, ncurses
+, re, ncurses
 , ppxlib, ppx_deriving
 , coqPackages
 , version ? "2.0.3"
 }:
 
-let p5 = camlp5; in
-let camlp5 = p5.override { legacy = true; }; in
-
 let fetched = coqPackages.metaFetch ({
     release."2.0.3".sha256 = "sha256-t2z0sWPiFgp6LuR6CsH/Zk9qfxW+3QjjFcYrB6qSPgc=";
     release."1.20.0".sha256 = "sha256-lctZAIQgOg5d+LfILtWsBVcsemV3zTZYfJfDlCxHtcA=";
@@ -38,11 +35,8 @@ buildDunePackage {
   minimalOCamlVersion = "4.07";
 
   # atdgen is both a library and executable
-  nativeBuildInputs = [ perl ]
-  ++ [ (if lib.versionAtLeast version "1.15" || version == "dev" then menhir else camlp5) ]
-  ++ lib.optional (lib.versionAtLeast version "1.16" || version == "dev") atdgen;
-  buildInputs = [ ncurses ]
-  ++ lib.optional (lib.versionAtLeast version "1.16" || version == "dev") atdgen;
+  nativeBuildInputs = [ menhir ] ++ [ atdgen ];
+  buildInputs = [ ncurses ] ++ [ atdgen ];
 
   propagatedBuildInputs = [ re stdlib-shims menhirLib ppxlib ppx_deriving ];