diff --git a/cmake/macros/IncludeBullet.cmake b/cmake/macros/IncludeBullet.cmake
index 56b6ce0ced..186e84d1ab 100644
--- a/cmake/macros/IncludeBullet.cmake
+++ b/cmake/macros/IncludeBullet.cmake
@@ -10,5 +10,7 @@
 macro(INCLUDE_BULLET)
     find_package(Bullet REQUIRED)
     include_directories("${BULLET_INCLUDE_DIRS}")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -isystem ${BULLET_INCLUDE_DIRS}")
+    if (APPLE OR UNIX)
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -isystem ${BULLET_INCLUDE_DIRS}")
+    endif()
 endmacro(INCLUDE_BULLET)