diff --git a/.github/workflows/unittest-mpich.yml b/.github/workflows/unittest-mpich.yml
index d3731c4d..a9049d17 100644
--- a/.github/workflows/unittest-mpich.yml
+++ b/.github/workflows/unittest-mpich.yml
@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         include:
-        - operating-system: macos-latest
+        - operating-system: macos-11
           python-version: '3.11'
           label: osx-64-py-3-11-mpich
           prefix: /Users/runner/miniconda3/envs/my-env
diff --git a/.github/workflows/unittest-openmpi.yml b/.github/workflows/unittest-openmpi.yml
index d375e9ca..7f37d0e7 100644
--- a/.github/workflows/unittest-openmpi.yml
+++ b/.github/workflows/unittest-openmpi.yml
@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         include:
-        - operating-system: macos-latest
+        - operating-system: macos-11
           python-version: '3.11'
           label: osx-64-py-3-11-openmpi
           prefix: /Users/runner/miniconda3/envs/my-env