diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 4b93e7f..e692fa7 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -25,10 +25,10 @@ jobs:
           authToken: ${{ secrets.CACHIX_AUTH_TOKEN }}
 
       - name: Build
-        run: nix-shell --run "xpg -v ${{ matrix.pg-version }} build"
+        run: nix-shell --argstr pgVersion "${{ matrix.pg-version }}" --arg cassert false --run "xpg -v ${{ matrix.pg-version }} build"
 
       - name: Run tests
-        run: nix-shell --run "xpg -v ${{ matrix.pg-version }} test"
+        run: nix-shell --argstr pgVersion "${{ matrix.pg-version }}" --arg cassert false --run "xpg -v ${{ matrix.pg-version }} test"
 
   test-on-macos:
     runs-on: macos-15
@@ -50,10 +50,10 @@ jobs:
           authToken: ${{ secrets.CACHIX_AUTH_TOKEN }}
 
       - name: Build
-        run: nix-shell --run "xpg -v ${{ matrix.pg-version }} build"
+        run: nix-shell --argstr pgVersion "${{ matrix.pg-version }}" --arg cassert false --run "xpg -v ${{ matrix.pg-version }} build"
 
       - name: Run tests
-        run: nix-shell --run "xpg -v ${{ matrix.pg-version }} test"
+        run: nix-shell --argstr pgVersion "${{ matrix.pg-version }}" --arg cassert false --run "xpg -v ${{ matrix.pg-version }} test"
 
   loadtest:
     runs-on: ubuntu-latest
@@ -78,11 +78,11 @@ jobs:
           authToken: ${{ secrets.CACHIX_AUTH_TOKEN }}
 
       - name: Build
-        run: nix-shell --run "xpg build"
+        run: nix-shell --argstr pgVersion "17" --arg cassert false --run "xpg build"
 
       - name: Run load test
         run: |
-          nix-shell --run "net-loadtest ${{ matrix.params.reqs }} ${{ matrix.params.batch }}" >> "$GITHUB_STEP_SUMMARY"
+          nix-shell --argstr pgVersion "17" --arg cassert false --run "net-loadtest ${{ matrix.params.reqs }} ${{ matrix.params.batch }}" >> "$GITHUB_STEP_SUMMARY"
 
   coverage:
     runs-on: ubuntu-latest
@@ -104,7 +104,7 @@ jobs:
           authToken: ${{ secrets.CACHIX_AUTH_TOKEN }}
 
       - name: Coverage
-        run: nix-shell --run "xpg -v ${{ matrix.pg-version }} coverage"
+        run: nix-shell --argstr pgVersion "${{ matrix.pg-version }}" --arg cassert false --run "xpg -v ${{ matrix.pg-version }} coverage"
 
       - name: Send coverage to Coveralls
         uses: coverallsapp/github-action@648a8eb78e6d50909eff900e4ec85cab4524a45b # v2.3.6
diff --git a/flake.lock b/flake.lock
index fa6f807..86062f8 100644
--- a/flake.lock
+++ b/flake.lock
@@ -43,16 +43,16 @@
         "nixpkgs": "nixpkgs_2"
       },
       "locked": {
-        "lastModified": 1782266378,
-        "narHash": "sha256-moRjdGvymGEyREU4++qpNzDuUN+nVC69CUYjhuY4Yzs=",
+        "lastModified": 1785529904,
+        "narHash": "sha256-DDIeJCHRtmvB7yocWTo1MISIGf0DsUmyLw6ISuEV4e0=",
         "owner": "steve-chavez",
         "repo": "xpg",
-        "rev": "d81725666a193c644fe0db96a988ece66edf460c",
+        "rev": "e7d47eb58f19168b5facc6b78a64f6cc7f04bbcb",
         "type": "github"
       },
       "original": {
         "owner": "steve-chavez",
-        "ref": "v2.4.0",
+        "ref": "v2.5.0",
         "repo": "xpg",
         "type": "github"
       }
diff --git a/flake.nix b/flake.nix
index a906059..f12922d 100644
--- a/flake.nix
+++ b/flake.nix
@@ -5,7 +5,7 @@
     # 2025-11-13
     nixpkgs.url = "github:NixOS/nixpkgs/91c9a64ce2a84e648d0cf9671274bb9c2fb9ba60";
     xpg = {
-      url = "github:steve-chavez/xpg/v2.4.0";
+      url = "github:steve-chavez/xpg/v2.5.0";
     };
   };
 
diff --git a/shell.nix b/shell.nix
index eecd3d5..ee568e9 100644
--- a/shell.nix
+++ b/shell.nix
@@ -14,6 +14,8 @@ in
     inherit (xpgLock) owner repo rev;
     sha256 = xpgLock.narHash;
   })
+, pgVersion ? null
+, cassert ? true
 }:
 let
   nginxCustom = pkgs.callPackage ./nix/nginxCustom.nix {};
@@ -36,7 +38,7 @@ in
 pkgs.mkShell {
   buildInputs =
     [
-      xpgPkgs.xpg
+      (if pgVersion == null then xpgPkgs.xpg else xpgPkgs.xpg.forVersions { versions = [ pgVersion ]; inherit cassert; })
       pythonDeps
       nginxCustom.nginxScript
       pkgs.curlWithGnuTls