diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 0d6b41efe..ac4e986e6 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -279,7 +279,7 @@ jobs:
             CXX: clang++
           - CC: gcc
             CXX: g++
-    runs-on: macos-11
+    runs-on: macos-10.15
     env:
       CC: ${{ matrix.CC }}
       CXX: ${{ matrix.CXX }}
diff --git a/.github/workflows/posix.yml b/.github/workflows/posix.yml
index b4b667be6..fc57a195d 100644
--- a/.github/workflows/posix.yml
+++ b/.github/workflows/posix.yml
@@ -225,7 +225,7 @@ jobs:
 
   pty-macos:
     name: pty-macos OT_DAEMON=${{ matrix.OT_DAEMON }}
-    runs-on: macos-11
+    runs-on: macos-10.15
     strategy:
       matrix:
         OT_DAEMON: ['off', 'on']