Index: sys/sys/mbuf.h
===================================================================
--- sys/sys/mbuf.h
+++ sys/sys/mbuf.h
@@ -1043,12 +1043,9 @@
 static __inline void
 m_align(struct mbuf *m, int len)
 {
-#ifdef INVARIANTS
-	const char *msg = "%s: not a virgin mbuf";
-#endif
 	int adjust;
 
-	KASSERT(m->m_data == M_START(m), (msg, __func__));
+	KASSERT(m->m_data == M_START(m), ("%s: not a virgin mbuf", __func__));
 
 	adjust = M_SIZE(m) - len;
 	m->m_data += adjust &~ (sizeof(long)-1);
Index: sys/sys/systm.h
===================================================================
--- sys/sys/systm.h
+++ sys/sys/systm.h
@@ -98,15 +98,26 @@
 #endif
 #endif
 
-#ifdef	INVARIANTS		/* The option is always available */
-#define	KASSERT(exp,msg) do {						\
+#ifdef INVARIANTS
+#define	_KASSERT_ESC(...)	__VA_ARGS__
+#define	_CAR_(first, ...)	first
+#define	_CAR(args)		_CAR_(args)
+#define	_CDR_(first, ...)	, ##__VA_ARGS__
+#define	_CDR(args)		_CDR_(args)
+
+#define	_KASSERT(fmt, ...)						\
+	kassert_panic("%s: " fmt, __VA_ARGS__)
+
+#define	KASSERT(exp, msg) do {						\
 	if (__predict_false(!(exp)))					\
-		kassert_panic msg;					\
+		_KASSERT(_CAR(_KASSERT_ESC msg), __func__		\
+		    _CDR(_KASSERT_ESC msg));				\
 } while (0)
 #define	VNASSERT(exp, vp, msg) do {					\
 	if (__predict_false(!(exp))) {					\
 		vn_printf(vp, "VNASSERT failed\n");			\
-		kassert_panic msg;					\
+		_KASSERT(_CAR(_KASSERT_ESC msg), __func__		\
+		    _CDR(_KASSERT_ESC msg));				\
 	}								\
 } while (0)
 #else