Index: sys/kern/uipc_mbuf.c
===================================================================
--- sys/kern/uipc_mbuf.c
+++ sys/kern/uipc_mbuf.c
@@ -120,6 +120,18 @@
 #endif
 
 /*
+ * Assert that the queue(3) macros produce code of the same size as an old
+ * plain pointer does.
+ */
+#ifdef INVARIANTS
+static struct mbuf m_assertbuf;
+CTASSERT(sizeof(m_assertbuf.m_slist) == sizeof(m_assertbuf.m_next));
+CTASSERT(sizeof(m_assertbuf.m_stailq) == sizeof(m_assertbuf.m_next));
+CTASSERT(sizeof(m_assertbuf.m_slistpkt) == sizeof(m_assertbuf.m_nextpkt));
+CTASSERT(sizeof(m_assertbuf.m_stailqpkt) == sizeof(m_assertbuf.m_nextpkt));
+#endif
+
+/*
  * m_get2() allocates minimum mbuf that would fit "size" argument.
  */
 struct mbuf *
Index: sys/sys/mbuf.h
===================================================================
--- sys/sys/mbuf.h
+++ sys/sys/mbuf.h
@@ -184,8 +184,16 @@
 	 * Compile-time assertions in uipc_mbuf.c test these values to ensure
 	 * that they are correct.
 	 */
-	struct mbuf	*m_next;	/* next buffer in chain */
-	struct mbuf	*m_nextpkt;	/* next chain in queue/record */
+	union {	/* next buffer in chain */
+		struct mbuf		*m_next;
+		SLIST_ENTRY(mbuf)	m_slist;
+		STAILQ_ENTRY(mbuf)	m_stailq;
+	};
+	union {	/* next chain in queue/record */
+		struct mbuf		*m_nextpkt;
+		SLIST_ENTRY(mbuf)	m_slistpkt;
+		STAILQ_ENTRY(mbuf)	m_stailqpkt;
+	};
 	caddr_t		 m_data;	/* location of data */
 	int32_t		 m_len;		/* amount of data in this mbuf */
 	uint32_t	 m_type:8,	/* type of data in this mbuf */