diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 92a9ff1..ec09a2e 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -23,9 +23,9 @@ jobs:
       fail-fast: false
       matrix:
         python-version: ["3.9"]
-        os: [ubuntu-latest, macos-latest]
+        os: [ubuntu-20.04, macos-latest]
         include:
-          - os: ubuntu-latest
+          - os: ubuntu-20.04
             INSTALL_DEPS: sudo apt-get update && sudo apt-get -y install gfortran-7 swig libopenmpi-dev openmpi-bin libopenblas-dev && sudo ln -s `which gfortran-7` /usr/local/bin/gfortran
           - os: macos-latest
             INSTALL_DEPS: brew update-reset && HOMEBREW_NO_AUTO_UPDATE=1  HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK=1 brew install gcc swig libomp open-mpi openblas && if [ ! -f /usr/local/bin/gfortran ]; then ln -s /usr/local/bin/gfortran-$(brew list --versions gcc | awk '{print $2}' | cut -d. -f1) /usr/local/bin/gfortran; fi
@@ -54,7 +54,4 @@ jobs:
           cd legacy_blinding
           python -m pip install --upgrade pip
           python -m pip install .
-
-      # Perform unit tests.
-      - name: Test legacy_blinding with pytest
-        run: pytest ./tests
+          pytest ./tests