diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index dea90e78c77a..542cb4600855 100644
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -294,9 +294,11 @@ m_demote(struct mbuf *m0, int all)
 }
 
 /*
- * Sanity checks on mbuf (chain).
- * Returns 0 bad, 1 good, panic worse.
- * sanitize, 0 run M_SANITY_ACTION, 1 garble things so they blow up later.
+ * Sanity checks on mbuf (chain) for use in KASSERT() and general
+ * debugging.
+ * Returns 0 or panics when bad and 1 on all tests passed.
+ * Sanitize, 0 to run M_SANITY_ACTION, 1 to garble things so they
+ * blow up later.
  */
 int
 m_sanity(struct mbuf *m0, int sanitize)
@@ -308,32 +310,31 @@ m_sanity(struct mbuf *m0, int sanitize)
 #define	M_SANITY_ACTION(s)	return (0)
 /* #define	M_SANITY_ACTION(s)	panic("mbuf %p: " s, m) */
 
-	m = m0;
-	while (m) {
+	for (m = m0; m != NULL; m = m->m_next) {
 		/*
 		 * Basic pointer checks.  If any of these fails then some
 		 * unrelated kernel memory before or after us is trashed.
 		 * No way to recover from that.
 		 */
-		a = (m->m_flags & M_EXT ? m->m_ext.ext_buf :
-			(m->m_flags & M_PKTHDR ? (caddr_t)(&m->m_pktdat) :
+		a = ((m->m_flags & M_EXT) ? m->m_ext.ext_buf :
+			((m->m_flags & M_PKTHDR) ? (caddr_t)(&m->m_pktdat) :
 			 (caddr_t)(&m->m_dat)) );
 		b = (caddr_t)(a + (m->m_flags & M_EXT ? m->m_ext.ext_size :
-			(m->m_flags & M_PKTHDR ? MHLEN : MLEN)));
+			((m->m_flags & M_PKTHDR) ? MHLEN : MLEN)));
 		if ((caddr_t)m->m_data < a)
 			M_SANITY_ACTION("m_data outside mbuf data range left");
 		if ((caddr_t)m->m_data > b)
 			M_SANITY_ACTION("m_data outside mbuf data range right");
 		if ((caddr_t)m->m_data + m->m_len > b)
 			M_SANITY_ACTION("m_data + m_len exeeds mbuf space");
-		if (m->m_flags & M_PKTHDR && m->m_pkthdr.header) {
+		if ((m->m_flags & M_PKTHDR) && m->m_pkthdr.header) {
 			if ((caddr_t)m->m_pkthdr.header < a ||
 			    (caddr_t)m->m_pkthdr.header > b)
 				M_SANITY_ACTION("m_pkthdr.header outside mbuf data range");
 		}
 
 		/* m->m_nextpkt may only be set on first mbuf in chain. */
-		if (m != m0 && m->m_nextpkt) {
+		if (m != m0 && m->m_nextpkt != NULL) {
 			if (sanitize) {
 				m_freem(m->m_nextpkt);
 				m->m_nextpkt = (struct mbuf *)0xDEADC0DE;
@@ -359,8 +360,7 @@ m_sanity(struct mbuf *m0, int sanitize)
 			if (sanitize) {
 				m_tag_delete_chain(m, NULL);
 				/* put in 0xDEADC0DE perhaps? */
-			}
-			else
+			} else
 				M_SANITY_ACTION("m_tags on in-chain mbuf");
 		}
 
@@ -373,18 +373,17 @@ m_sanity(struct mbuf *m0, int sanitize)
 			} else
 				M_SANITY_ACTION("M_PKTHDR on in-chain mbuf");
 		}
-
-		m = m->m_next;
 	}
-	if (pktlen && pktlen != m0->m_pkthdr.len) {
+	m = m0;
+	if (pktlen && pktlen != m->m_pkthdr.len) {
 		if (sanitize)
-			m0->m_pkthdr.len = 0;
+			m->m_pkthdr.len = 0;
 		else
 			M_SANITY_ACTION("m_pkthdr.len != mbuf chain length");
 	}
-#undef	M_SANITY_ACTION
-
 	return 1;
+
+#undef	M_SANITY_ACTION
 }