diff --git a/CMakeLists.txt b/CMakeLists.txt
index e0455521cecef21c94c10ab39421fe56930d84b7..1288cd3c62ec95a1c7652ff38074b8332830ea5d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,6 +18,7 @@ set(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/CMakeModules)
 include (CorsikaUtilities) # a few cmake function
 
 set (CMAKE_CXX_STANDARD 17)
+set (CMAKE_CXX_EXTENSIONS OFF)
 enable_testing ()
 set (CTEST_OUTPUT_ON_FAILURE 1)