diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -526,8 +526,8 @@
     set(LIBCXX_STANDARD_VER c++11 CACHE STRING "internal option to change build dialect")
   endif()
   target_add_compile_flags_if_supported(${target} PRIVATE -std=${LIBCXX_STANDARD_VER})
-  target_add_compile_flags_if_supported(${target} PRIVATE "/std:${LIBCXX_STANDARD_VER}")
   mangle_name("LIBCXX_SUPPORTS_STD_EQ_${LIBCXX_STANDARD_VER}_FLAG" SUPPORTS_DIALECT_NAME)
+  target_add_compile_flags_if_supported(${target} PRIVATE "/std:${LIBCXX_STANDARD_VER}")
   mangle_name("LIBCXX_SUPPORTS_STD_COLON_${LIBCXX_STANDARD_VER}_FLAG" SUPPORTS_DIALECT_NAME_MSVC)
   if(NOT ${SUPPORTS_DIALECT_NAME} AND NOT ${SUPPORTS_DIALECT_NAME_MSVC})
     if(NOT "${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" AND NOT "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")