diff --git a/src/xpdev/Common.bmake b/src/xpdev/Common.bmake
index 84d152df1eedf21bf1516214c424627cf33e347d..b22d0f532fae3358ae591bdd7dd4bbb11d4fb20b 100644
--- a/src/xpdev/Common.bmake
+++ b/src/xpdev/Common.bmake
@@ -1,3 +1,4 @@
+XPDEV-MT_CFLAGS = $(XPDEV-MT_CFLAGS) -DXPDEV_THREAD_SAFE
 !ifdef USE_SDL
 XPDEV-MT_CFLAGS = $(XPDEV-MT_CFLAGS) -DWITH_SDL -DWIN32 -I../../include/sdl
 XPDEV_CFLAGS = $(XPDEV_CFLAGS) -DWITH_SDL -DWIN32 -I../../include/sdl