diff --git a/tools/ci/gha-install.py b/tools/ci/gha-install.py
index 4cc85671d..4c69ba70b 100644
--- a/tools/ci/gha-install.py
+++ b/tools/ci/gha-install.py
@@ -34,7 +34,7 @@ def install(omp=False, mpi=False, phdf5=False, dagmc=False, libmesh=False):
 
     # Use MPI wrappers when building in parallel
     if mpi:
-        os.environ['CXX'] = 'mpicxx'
+        cmake_cmd.append('-DOPENMC_USE_MPI=on')
 
     # Tell CMake to prefer parallel HDF5 if specified
     if phdf5:
diff --git a/tools/ci/gha-install.sh b/tools/ci/gha-install.sh
index aa40eb90b..52e71b693 100755
--- a/tools/ci/gha-install.sh
+++ b/tools/ci/gha-install.sh
@@ -32,7 +32,6 @@ fi
 if [[ $MPI == 'y' ]]; then
     pip install --no-binary=mpi4py mpi4py
 
-    export CC=mpicc
     export HDF5_MPI=ON
     export HDF5_DIR=/usr/lib/x86_64-linux-gnu/hdf5/mpich
     pip install --no-binary=h5py h5py