diff --git a/sys/kern/uipc_sockbuf.c b/sys/kern/uipc_sockbuf.c
index 8e99f3e3899d..d804d9ae3f39 100644
--- a/sys/kern/uipc_sockbuf.c
+++ b/sys/kern/uipc_sockbuf.c
@@ -620,29 +620,12 @@ sbappendrecord(struct sockbuf *sb, struct mbuf *m0)
 	SOCKBUF_UNLOCK(sb);
 }
 
-/*
- * Append address and data, and optionally, control (ancillary) data to the
- * receive queue of a socket.  If present, m0 must include a packet header
- * with total length.  Returns 0 if no space in sockbuf or insufficient
- * mbufs.
- */
-int
-sbappendaddr_locked(struct sockbuf *sb, const struct sockaddr *asa,
-    struct mbuf *m0, struct mbuf *control)
+/* Helper routine that appends data, control, and address to a sockbuf. */
+static int
+sbappendaddr_locked_internal(struct sockbuf *sb, const struct sockaddr *asa,
+    struct mbuf *m0, struct mbuf *control, struct mbuf *ctrl_last)
 {
 	struct mbuf *m, *n, *nlast;
-	int space = asa->sa_len;
-
-	SOCKBUF_LOCK_ASSERT(sb);
-
-	if (m0 && (m0->m_flags & M_PKTHDR) == 0)
-		panic("sbappendaddr_locked");
-	if (m0)
-		space += m0->m_pkthdr.len;
-	space += m_length(control, &n);
-
-	if (space > sbspace(sb))
-		return (0);
 #if MSIZE <= 256
 	if (asa->sa_len > MLEN)
 		return (0);
@@ -652,8 +635,8 @@ sbappendaddr_locked(struct sockbuf *sb, const struct sockaddr *asa,
 		return (0);
 	m->m_len = asa->sa_len;
 	bcopy(asa, mtod(m, caddr_t), asa->sa_len);
-	if (n)
-		n->m_next = m0;		/* concatenate data to control */
+	if (ctrl_last)
+		ctrl_last->m_next = m0;	/* concatenate data to control */
 	else
 		control = m0;
 	m->m_next = control;
@@ -670,6 +653,50 @@ sbappendaddr_locked(struct sockbuf *sb, const struct sockaddr *asa,
 	return (1);
 }
 
+/*
+ * Append address and data, and optionally, control (ancillary) data to the
+ * receive queue of a socket.  If present, m0 must include a packet header
+ * with total length.  Returns 0 if no space in sockbuf or insufficient
+ * mbufs.
+ */
+int
+sbappendaddr_locked(struct sockbuf *sb, const struct sockaddr *asa,
+    struct mbuf *m0, struct mbuf *control)
+{
+	struct mbuf *ctrl_last;
+	int space = asa->sa_len;
+
+	SOCKBUF_LOCK_ASSERT(sb);
+
+	if (m0 && (m0->m_flags & M_PKTHDR) == 0)
+		panic("sbappendaddr_locked");
+	if (m0)
+		space += m0->m_pkthdr.len;
+	space += m_length(control, &ctrl_last);
+
+	if (space > sbspace(sb))
+		return (0);
+	return (sbappendaddr_locked_internal(sb, asa, m0, control, ctrl_last));
+}
+
+/*
+ * Append address and data, and optionally, control (ancillary) data to the
+ * receive queue of a socket.  If present, m0 must include a packet header
+ * with total length.  Returns 0 if insufficient mbufs.  Does not validate space
+ * on the receiving sockbuf.
+ */
+int
+sbappendaddr_nospacecheck_locked(struct sockbuf *sb, const struct sockaddr *asa,
+    struct mbuf *m0, struct mbuf *control)
+{
+	struct mbuf *ctrl_last;
+
+	SOCKBUF_LOCK_ASSERT(sb);
+
+	ctrl_last = (control == NULL) ? NULL : m_last(control);
+	return (sbappendaddr_locked_internal(sb, asa, m0, control, ctrl_last));
+}
+
 /*
  * Append address and data, and optionally, control (ancillary) data to the
  * receive queue of a socket.  If present, m0 must include a packet header
diff --git a/sys/kern/uipc_usrreq.c b/sys/kern/uipc_usrreq.c
index e1eee36e45ed..676029a689d5 100644
--- a/sys/kern/uipc_usrreq.c
+++ b/sys/kern/uipc_usrreq.c
@@ -892,7 +892,8 @@ uipc_send(struct socket *so, int flags, struct mbuf *m, struct sockaddr *nam,
 			from = &sun_noname;
 		so2 = unp2->unp_socket;
 		SOCKBUF_LOCK(&so2->so_rcv);
-		if (sbappendaddr_locked(&so2->so_rcv, from, m, control)) {
+		if (sbappendaddr_nospacecheck_locked(&so2->so_rcv, from, m,
+		    control)) {
 			sorwakeup_locked(so2);
 			m = NULL;
 			control = NULL;
@@ -977,8 +978,14 @@ uipc_send(struct socket *so, int flags, struct mbuf *m, struct sockaddr *nam,
 			const struct sockaddr *from;
 
 			from = &sun_noname;
-			if (sbappendaddr_locked(&so2->so_rcv, from, m,
-			    control))
+			/*
+			 * Don't check for space available in so2->so_rcv.
+			 * Unix domain sockets only check for space in the
+			 * sending sockbuf, and that check is performed one
+			 * level up the stack.
+			 */
+			if (sbappendaddr_nospacecheck_locked(&so2->so_rcv,
+				from, m, control))
 				control = NULL;
 			break;
 			}
diff --git a/sys/sys/sockbuf.h b/sys/sys/sockbuf.h
index e7162418e67b..6994fd3fd60f 100644
--- a/sys/sys/sockbuf.h
+++ b/sys/sys/sockbuf.h
@@ -127,6 +127,8 @@ int	sbappendaddr(struct sockbuf *sb, const struct sockaddr *asa,
 	    struct mbuf *m0, struct mbuf *control);
 int	sbappendaddr_locked(struct sockbuf *sb, const struct sockaddr *asa,
 	    struct mbuf *m0, struct mbuf *control);
+int	sbappendaddr_nospacecheck_locked(struct sockbuf *sb,
+	    const struct sockaddr *asa, struct mbuf *m0, struct mbuf *control);
 int	sbappendcontrol(struct sockbuf *sb, struct mbuf *m0,
 	    struct mbuf *control);
 int	sbappendcontrol_locked(struct sockbuf *sb, struct mbuf *m0,
diff --git a/tests/sys/kern/unix_seqpacket_test.c b/tests/sys/kern/unix_seqpacket_test.c
index f2904aec060b..51769c4abd42 100644
--- a/tests/sys/kern/unix_seqpacket_test.c
+++ b/tests/sys/kern/unix_seqpacket_test.c
@@ -361,6 +361,12 @@ test_pipe(size_t sndbufsize, size_t rcvbufsize)
 	reader_data.so = sv[1];
 	ATF_REQUIRE_EQ(0, pthread_create(&writer, NULL, test_pipe_writer,
 	    				 (void*)&writer_data));
+	/* 
+	 * Give the writer time to start writing, and hopefully block, before
+	 * starting the reader.  This increases the likelihood of the test case
+	 * failing due to PR kern/185812
+	 */
+	usleep(1000);
 	ATF_REQUIRE_EQ(0, pthread_create(&reader, NULL, test_pipe_reader,
 	    				 (void*)&reader_data));
 
@@ -951,7 +957,6 @@ ATF_TC_BODY(pipe_simulator_8k_128k, tc)
 ATF_TC_WITHOUT_HEAD(pipe_simulator_128k_8k);
 ATF_TC_BODY(pipe_simulator_128k_8k, tc)
 {
-	atf_tc_expect_fail("PR kern/185812 SOCK_SEQPACKET AF_UNIX sockets with asymmetrical buffers drop packets");
 	test_pipe_simulator(131072, 8192);
 }