diff --git a/.github/workflows/build_python_3.9.1.yml b/.github/workflows/build_python_3.9.1.yml
index 9a51e2b..66166b9 100644
--- a/.github/workflows/build_python_3.9.1.yml
+++ b/.github/workflows/build_python_3.9.1.yml
@@ -13,7 +13,7 @@ on:
 
 jobs:
   build:
-    runs-on: macos-latest
+    runs-on: macos-11.0
 
     steps:
     - name: Set environment variables