diff --git a/.github/workflows/mac-test.yml b/.github/workflows/mac-test.yml
index 5853e5353ca..43ca3d4a486 100644
--- a/.github/workflows/mac-test.yml
+++ b/.github/workflows/mac-test.yml
@@ -21,7 +21,7 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
     - run: |
-        brew install fftw openssl
+        brew install fftw openssl gsl
         pip install --upgrade pip setuptools "tox<4.0.0"
     - name: run basic pycbc test suite
       run: |