diff --git a/cmake/CXXSniffer.cmake b/cmake/CXXSniffer.cmake
index 07c06cdae..ef1ec6511 100644
--- a/cmake/CXXSniffer.cmake
+++ b/cmake/CXXSniffer.cmake
@@ -6,7 +6,8 @@ include (CheckCXXCompilerFlag)
 CHECK_CXX_COMPILER_FLAG("-std=c++17"   _HAS_CXX17)
 
 if (_HAS_CXX17)
-  set (_CXX14_FLAGS "-std=c++17")
+  set (CMAKE_CXX_STANDARD 17)
+  set (CMAKE_CXX_EXTENSIONS OFF)
 else (_HAS_CXX17)
  message (FATAL_ERROR "C++17 support missing. Try upgrading your C++ compiler. If you have a good reason for using an outdated compiler, please let us know at support@gothenburgbitfactory.org.")
 endif (_HAS_CXX17)
@@ -32,7 +33,7 @@ elseif (${CMAKE_SYSTEM_NAME} STREQUAL "GNU")
   set (GNUHURD true)
 elseif (${CMAKE_SYSTEM_NAME} STREQUAL "CYGWIN")
   set (CYGWIN true)
-  set (_CXX14_FLAGS "-std=gnu++17")
+  set (CMAKE_CXX_EXTENSIONS ON)
 else (${CMAKE_SYSTEM_NAME} MATCHES "Linux")
   set (UNKNOWN true)
 endif (${CMAKE_SYSTEM_NAME} MATCHES "Linux")