diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
--- a/flang/CMakeLists.txt
+++ b/flang/CMakeLists.txt
@@ -37,13 +37,7 @@
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
 include(AddFlang)
 
-if (MSVC)
-  set(_FLANG_ENABLE_WERROR_DEFAULT OFF)
-else ()
-  set(_FLANG_ENABLE_WERROR_DEFAULT ON)
-endif()
-option(FLANG_ENABLE_WERROR "Fail and stop building flang if a warning is triggered."
-       "${_FLANG_ENABLE_WERROR_DEFAULT}")
+option(FLANG_ENABLE_WERROR "Fail and stop building flang if a warning is triggered." OFF)
 
 # Check for a standalone build and configure as appropriate from
 # there.
@@ -305,9 +299,6 @@
     append("-Werror" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
     append("-Wno-error" CMAKE_REQUIRED_FLAGS)
   endif( LLVM_COMPILER_IS_GCC_COMPATIBLE )
-  if (NOT LLVM_ENABLE_WERROR)
-      message(WARNING "FLANG_ENABLE_WERROR setting is different from LLVM_ENABLE_WERROR.")
-  endif()
 endif()
 
 # Builtin check_cxx_compiler_flag doesn't seem to work correctly