diff --git a/sys/sys/sx.h b/sys/sys/sx.h
--- a/sys/sys/sx.h
+++ b/sys/sys/sx.h
@@ -303,7 +303,7 @@
 /* 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_xunlock(s)	do {} while (0)
 #define SX_DUPOK 0
 #define SX_NEW 0
 #define SX_NOWITNESS 0