diff --git a/.github/workflows/amd64_macos_bazel.yml b/.github/workflows/amd64_macos_bazel.yml
index fd1bc5a..8ad2f7c 100644
--- a/.github/workflows/amd64_macos_bazel.yml
+++ b/.github/workflows/amd64_macos_bazel.yml
@@ -1,3 +1,4 @@
+# ref: https://github.com/actions/runner-images
 name: amd64 MacOS Bazel
 
 on:
@@ -10,7 +11,7 @@ on:
 jobs:
   # Building using the github runner environement directly.
   bazel:
-    runs-on: macos-latest
+    runs-on: macos-13 # Using x86 processors, ref: https://github.com/actions/runner-images
     steps:
       - name: Check out repository code
         uses: actions/checkout@v3
diff --git a/.github/workflows/amd64_macos_cmake.yml b/.github/workflows/amd64_macos_cmake.yml
index 3756500..b5946af 100644
--- a/.github/workflows/amd64_macos_cmake.yml
+++ b/.github/workflows/amd64_macos_cmake.yml
@@ -1,3 +1,4 @@
+# ref: https://github.com/actions/runner-images
 name: amd64 MacOS CMake
 
 on:
@@ -10,7 +11,7 @@ on:
 jobs:
   # Building using the github runner environement directly.
   xcode:
-    runs-on: macos-latest
+    runs-on: macos-13 # Using x86 processors, ref: https://github.com/actions/runner-images
     env:
       CTEST_OUTPUT_ON_FAILURE: 1
     steps:
@@ -26,7 +27,7 @@ jobs:
     - name: Install
       run: cmake --build build --config Release --target install -v
   make:
-    runs-on: macos-latest
+    runs-on: macos-13 # Using x86 processors, ref: https://github.com/actions/runner-images
     env:
       CTEST_OUTPUT_ON_FAILURE: 1
     steps: