diff --git a/gdtoa/CMakeLists.txt b/gdtoa/CMakeLists.txt
index c165422834..4dff4c30db 100644
--- a/gdtoa/CMakeLists.txt
+++ b/gdtoa/CMakeLists.txt
@@ -8,8 +8,8 @@ if( MSVC )
 	set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /wd4554 /wd4102" )
 endif()
 
-if( ZD_CMAKE_COMPILER_IS_GNUCXX_COMPATIBLE )
-	set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra" )
+if( ZD_CMAKE_COMPILER_IS_GNUC_COMPATIBLE )
+	set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra" )
 endif()
 
 # Enable fast flag for gdtoa