diff --git a/CMakeLists.txt b/CMakeLists.txt
index 66f4d0363..362ca8d56 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -71,16 +71,18 @@ function (die msg)
 endfunction ()
 
 function (add_c_flag_if_supported flag var)
-  string(REPLACE "-" "_" supported ${flag}_c)
-  check_c_compiler_flag(${flag} ${supported})
+  set(TMP "-Werror ${flag}")
+  string(REGEX REPLACE "[- ]" "_" supported ${TMP}_c)
+  check_c_compiler_flag(${TMP} ${supported})
   if(${${supported}})
     set(${var} "${${var}} ${flag}" PARENT_SCOPE)
   endif()
 endfunction()
 
 function (add_cxx_flag_if_supported flag var)
-  string(REPLACE "-" "_" supported ${flag}_cxx)
-  check_cxx_compiler_flag(${flag} ${supported})
+  set(TMP "-Werror ${flag}")
+  string(REGEX REPLACE "[- ]" "_" supported ${TMP}_cxx)
+  check_cxx_compiler_flag(${TMP} ${supported})
   if(${${supported}})
     set(${var} "${${var}} ${flag}" PARENT_SCOPE)
   endif()