diff --git a/sys/sys/sx.h b/sys/sys/sx.h
--- a/sys/sys/sx.h
+++ b/sys/sys/sx.h
@@ -301,12 +301,12 @@
 
 #ifdef _STANDALONE
 /* since we have no threads in the boot loader, trivially implement no-op version */
-#define sx_xlock(s) (1)
-#define sx_try_xlock(s) (1)
-#define sx_xunlock(s) (1)
-#define SX_DUPOK 0
-#define SX_NEW 0
-#define SX_NOWITNESS 0
+#define	sx_xlock(s)	do {} while (0)
+#define	sx_try_xlock(s)	(1)
+#define	sx_xunlock(s)	do {} while (0)
+#define	SX_DUPOK	0
+#define	SX_NEW		0
+#define	SX_NOWITNESS	0
 
 static __inline void
 sx_init_flags(struct sx *sx, const char *description, int opts)