diff --git a/Modules/Compiler/IAR-CXX.cmake b/Modules/Compiler/IAR-CXX.cmake
index 7df74ad412..6c15735e7f 100644
--- a/Modules/Compiler/IAR-CXX.cmake
+++ b/Modules/Compiler/IAR-CXX.cmake
@@ -19,12 +19,14 @@ if(NOT CMAKE_IAR_CXX_FLAG)
   cmake_policy(PUSH)
   cmake_policy(SET CMP0057 NEW) # if IN_LIST
 
-  if(${CMAKE_CXX_STANDARD_COMPUTED_DEFAULT} IN_LIST "14;17" OR
+  set(_CMAKE_IAR_MODERNCXX_LIST 14 17)
+  if(${CMAKE_CXX_STANDARD_COMPUTED_DEFAULT} IN_LIST _CMAKE_IAR_MODERNCXX_LIST OR
      ("${CMAKE_CXX_COMPILER_ARCHITECTURE_ID}" STREQUAL "ARM" AND ${CMAKE_CXX_STANDARD_COMPUTED_DEFAULT} EQUAL 98))
     string(PREPEND CMAKE_CXX_FLAGS "--c++ ")
   else()
     string(PREPEND CMAKE_CXX_FLAGS "--eec++ ")
   endif()
+  unset(_CMAKE_IAR_MODERNCXX_LIST)
 
   cmake_policy(POP)
 endif()