diff --git a/.github/workflows/mac.yml b/.github/workflows/mac.yml
index 871f80919..27162254d 100644
--- a/.github/workflows/mac.yml
+++ b/.github/workflows/mac.yml
@@ -15,7 +15,7 @@ jobs:
       run: |
         mkdir build
         cd build
-        cmake -GNinja -DDD4HEP_USE_GEANT4=OFF -DBoost_NO_BOOST_CMAKE=ON -DDD4HEP_USE_LCIO=OFF -DBUILD_TESTING=ON -DDD4HEP_USE_XERCESC=OFF -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_STANDARD=20 -DDD4HEP_RELAX_PYVER=ON ..
+        cmake -GNinja -DDD4HEP_USE_GEANT4=OFF -DBoost_NO_BOOST_CMAKE=ON -DDD4HEP_USE_LCIO=OFF -DBUILD_TESTING=ON -DDD4HEP_USE_XERCESC=OFF -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_STANDARD=17 -DDD4HEP_RELAX_PYVER=ON ..
         ninja
         ninja install
         . ../bin/thisdd4hep.sh
@@ -23,7 +23,7 @@ jobs:
         cd ../examples/
         mkdir build
         cd build
-        cmake -GNinja -DBoost_NO_BOOST_CMAKE=ON -DDD4HEP_USE_XERCESC=OFF -DCMAKE_CXX_STANDARD=20 ..
+        cmake -GNinja -DBoost_NO_BOOST_CMAKE=ON -DDD4HEP_USE_XERCESC=OFF -DCMAKE_CXX_STANDARD=17 ..
         ninja
         ninja install
         ctest --output-on-failure -E t_ClientTests_Check_Shape_Eightpoint_Reflect_DetElement