diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 00a07f5..7944c2c 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -64,14 +64,14 @@ jobs:
           --allowed-uris https://static.rust-lang.org \
           --option restrict-eval true \
           --option allow-import-from-derivation true \
-          --drv-path --show-trace \
+          --drv-path --show-trace --impure \
           -I nixpkgs=$(nix-instantiate --find-file nixpkgs) \
           -I $PWD
     - name: Build nix packages
       env:
         NIXPKGS_ALLOW_UNFREE: 1
         NIXPKGS_ALLOW_INSECURE: 1
-      run: nix shell -f '<nixpkgs>' nix-build-uncached -c nix-build-uncached ci.nix -A cacheOutputs
+      run: nix shell --impure -f '<nixpkgs>' nix-build-uncached -c nix-build-uncached ci.nix -A cacheOutputs
     - name: Trigger NUR update
       # Don't replace <YOUR_REPO_NAME> here!
       if: ${{ matrix.nurRepo != '<YOUR_REPO_NAME>' }}
diff --git a/pkgs/hpc/conveyorlc/default.nix b/pkgs/hpc/conveyorlc/default.nix
index 1097170..80b2b35 100644
--- a/pkgs/hpc/conveyorlc/default.nix
+++ b/pkgs/hpc/conveyorlc/default.nix
@@ -12,12 +12,17 @@
 let
    onOffBool = b: if b then "ON" else "OFF";
    boost = pkgs.boost172.override { useMpi = true; };
+    oldpkgs = import (builtins.fetchTarball {
+        url = "https://github.com/NixOS/nixpkgs/archive/d1c3fea7ecbed758168787fe4e4a3157e52bc808.tar.gz";
+    }) {};
+
+    openmpi = oldpkgs.openmpi;
 in
 
 
 stdenv.mkDerivation rec {
   pname = "conveyorlc";
-  version = "1.1.2-1";
+  version = "1.1.2-2";
 
   # Updated when we have final versioned release - still a WIP
   # src = fetchurl {
@@ -35,7 +40,7 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [cmake pkgs.extra-cmake-modules];
   buildInputs = [
       boost
-      pkgs.openmpi
+      openmpi
       pkgs.openbabel2
       pkgs.zlib
       pkgs.hdf5-cpp