diff --git a/sys/sys/sx.h b/sys/sys/sx.h
index 0612b7bf37b7..43f89fba5099 100644
--- a/sys/sys/sx.h
+++ b/sys/sys/sx.h
@@ -82,6 +82,13 @@ struct sx_args {
 #define	sx_xunlock(sx)		_sx_xunlock((sx), LOCK_FILE, LOCK_LINE)
 #define	sx_try_upgrade(sx)	_sx_try_upgrade((sx), LOCK_FILE, LOCK_LINE)
 #define	sx_downgrade(sx)	_sx_downgrade((sx), LOCK_FILE, LOCK_LINE)
+#define	sx_unlock(sx)	\
+		do { \
+			if ((sx)->sx_cnt < 0) \
+				sx_xunlock(sx); \
+			else \
+				sx_sunlock(sx); \
+		} while (0)
 
 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
 #define	SX_LOCKED		LA_LOCKED