diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index bcf4b83..4f93d6e 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -114,6 +114,11 @@ jobs:
       run: |
           sudo ln -s /usr/local/opt/openssl@1.1  /usr/local/ssl
 
+    - name: Install gfortan-9 (MacOSX)
+      if: ${{ matrix.config.name == 'MacOSX'}}
+      run: |
+          brew install gcc@9
+
     - name: Make build directory
       run: |
           mkdir build