diff --git a/CMakeLists.txt b/CMakeLists.txt
index 79e0152ef..dbbd097b9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -99,7 +99,7 @@ else()
   endif()
   if(MINGW)
     set(WARNINGS "${WARNINGS} -Wno-error=unused-value -Wno-error=unused-but-set-variable")
-    set(MINGW_FLAG "-DWIN32_LEAN_AND_MEAN")
+    set(MINGW_FLAG "${MINGW_FLAG} -DWIN32_LEAN_AND_MEAN")
     include_directories(SYSTEM src/platform/mingw)
   else()
     set(MINGW_FLAG "")