diff --git a/src/vm.c b/src/vm.c
index c6aa92135..5d7fb6072 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -326,7 +326,10 @@ argnum_error(mrb_state *mrb, int num)
   (r).value.p = (void*)(v);\
 }
 
+#ifdef __GNUC__
 #define DIRECT_THREADED
+#endif
+
 #ifndef DIRECT_THREADED
 
 #define INIT_DISPACTH for (;;) { i = *pc; switch (GET_OPCODE(i)) {