diff --git a/.github/workflows/unittestlib.yml b/.github/workflows/unittestlib.yml
index 7b73327f97..a53c67a75b 100644
--- a/.github/workflows/unittestlib.yml
+++ b/.github/workflows/unittestlib.yml
@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-latest, ubuntu-20.04, ubuntu-22.04]
+        os: [macos-13, ubuntu-20.04, ubuntu-22.04]
         ruby: [2.7, 3.1]
         # 2.7 not supported on 22.04
         exclude: