diff --git a/CHANGES b/CHANGES
index fd058c7b04..c5480469fe 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,5 @@
+4950.	[bug]		ISC_SOCKEVENTATTR_TRUNC was not be set. [GL #238]
+
 4949.	[bug]		lib/isc/print.c failed to handle floating point
 			output correctly. [GL #261]
 
diff --git a/lib/isc/tests/socket_test.c b/lib/isc/tests/socket_test.c
index 8122e1bcc1..c9a1571973 100644
--- a/lib/isc/tests/socket_test.c
+++ b/lib/isc/tests/socket_test.c
@@ -28,6 +28,7 @@
 
 static isc_boolean_t recv_dscp;
 static unsigned int recv_dscp_value;
+static isc_boolean_t recv_trunc;
 
 /*
  * Helper functions
@@ -73,8 +74,10 @@ event_done(isc_task_t *task, isc_event_t *event) {
 	if ((dev->attributes & ISC_SOCKEVENTATTR_DSCP) != 0) {
 		recv_dscp = ISC_TRUE;
 		recv_dscp_value = dev->dscp;;
-	} else
+	} else {
 		recv_dscp = ISC_FALSE;
+	}
+	recv_trunc = ISC_TF((dev->attributes & ISC_SOCKEVENTATTR_TRUNC) != 0);
 	isc_event_free(&event);
 }
 
@@ -777,6 +780,131 @@ ATF_TC_BODY(net_probedscp, tc) {
 #endif
 }
 
+/* Test UDP truncation detection */
+ATF_TC(udp_trunc);
+ATF_TC_HEAD(udp_trunc, tc) {
+	atf_tc_set_md_var(tc, "descr", "UDP Truncation detection");
+}
+ATF_TC_BODY(udp_trunc, tc) {
+	isc_result_t result;
+	isc_sockaddr_t addr1, addr2;
+	struct in_addr in;
+	isc_socket_t *s1 = NULL, *s2 = NULL;
+	isc_task_t *task = NULL;
+	char sendbuf[BUFSIZ*2], recvbuf[BUFSIZ];
+	completion_t completion;
+	isc_region_t r;
+	isc_socketevent_t *socketevent;
+
+	UNUSED(tc);
+
+	result = isc_test_begin(NULL, ISC_TRUE, 0);
+	ATF_REQUIRE_EQ(result, ISC_R_SUCCESS);
+
+	in.s_addr = inet_addr("127.0.0.1");
+	isc_sockaddr_fromin(&addr1, &in, 0);
+	isc_sockaddr_fromin(&addr2, &in, 0);
+
+	result = isc_socket_create(socketmgr, PF_INET, isc_sockettype_udp, &s1);
+	ATF_CHECK_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			   isc_result_totext(result));
+	result = isc_socket_bind(s1, &addr1, ISC_SOCKET_REUSEADDRESS);
+	ATF_CHECK_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			   isc_result_totext(result));
+	result = isc_socket_getsockname(s1, &addr1);
+	ATF_CHECK_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			 isc_result_totext(result));
+	ATF_REQUIRE(isc_sockaddr_getport(&addr1) != 0);
+
+	result = isc_socket_create(socketmgr, PF_INET, isc_sockettype_udp, &s2);
+	ATF_CHECK_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			   isc_result_totext(result));
+	result = isc_socket_bind(s2, &addr2, ISC_SOCKET_REUSEADDRESS);
+	ATF_CHECK_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			   isc_result_totext(result));
+	result = isc_socket_getsockname(s2, &addr2);
+	ATF_CHECK_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			 isc_result_totext(result));
+	ATF_REQUIRE(isc_sockaddr_getport(&addr2) != 0);
+
+	result = isc_task_create(taskmgr, 0, &task);
+	ATF_CHECK_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			   isc_result_totext(result));
+
+	/*
+	 * Send a message that will not be truncated.
+	 */
+	memset(sendbuf, 0xff, sizeof(sendbuf));
+	snprintf(sendbuf, sizeof(sendbuf), "Hello");
+	r.base = (void *) sendbuf;
+	r.length = strlen(sendbuf) + 1;
+
+	completion_init(&completion);
+
+	socketevent = isc_socket_socketevent(mctx, s1, ISC_SOCKEVENT_SENDDONE,
+					     event_done, &completion);
+	ATF_REQUIRE(socketevent != NULL);
+
+	result = isc_socket_sendto2(s1, &r, task, &addr2, NULL, socketevent, 0);
+	ATF_REQUIRE_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			   isc_result_totext(result));
+	waitfor(&completion);
+	ATF_CHECK(completion.done);
+	ATF_CHECK_EQ(completion.result, ISC_R_SUCCESS);
+
+	r.base = (void *) recvbuf;
+	r.length = BUFSIZ;
+	completion_init(&completion);
+	recv_trunc = ISC_FALSE;
+	result = isc_socket_recv(s2, &r, 1, task, event_done, &completion);
+	ATF_CHECK_EQ(result, ISC_R_SUCCESS);
+	waitfor(&completion);
+	ATF_CHECK(completion.done);
+	ATF_CHECK_EQ(completion.result, ISC_R_SUCCESS);
+	ATF_CHECK_STREQ(recvbuf, "Hello");
+	ATF_CHECK_EQ(recv_trunc, ISC_FALSE);
+
+	/*
+	 * Send a message that will be truncated.
+	 */
+	memset(sendbuf, 0xff, sizeof(sendbuf));
+	snprintf(sendbuf, sizeof(sendbuf), "Hello");
+	r.base = (void *) sendbuf;
+	r.length = sizeof(sendbuf);
+
+	completion_init(&completion);
+
+	socketevent = isc_socket_socketevent(mctx, s1, ISC_SOCKEVENT_SENDDONE,
+					     event_done, &completion);
+	ATF_REQUIRE(socketevent != NULL);
+
+	result = isc_socket_sendto2(s1, &r, task, &addr2, NULL, socketevent, 0);
+	ATF_REQUIRE_EQ_MSG(result, ISC_R_SUCCESS, "%s",
+			   isc_result_totext(result));
+	waitfor(&completion);
+	ATF_CHECK(completion.done);
+	ATF_CHECK_EQ(completion.result, ISC_R_SUCCESS);
+
+	r.base = (void *) recvbuf;
+	r.length = BUFSIZ;
+	completion_init(&completion);
+	recv_trunc = ISC_FALSE;
+	result = isc_socket_recv(s2, &r, 1, task, event_done, &completion);
+	ATF_CHECK_EQ(result, ISC_R_SUCCESS);
+	waitfor(&completion);
+	ATF_CHECK(completion.done);
+	ATF_CHECK_EQ(completion.result, ISC_R_SUCCESS);
+	ATF_CHECK_STREQ(recvbuf, "Hello");
+	ATF_CHECK_EQ(recv_trunc, ISC_TRUE);
+
+	isc_task_detach(&task);
+
+	isc_socket_detach(&s1);
+	isc_socket_detach(&s2);
+
+	isc_test_end();
+}
+
 /*
  * Main
  */
@@ -788,6 +916,7 @@ ATF_TP_ADD_TCS(tp) {
 	ATF_TP_ADD_TC(tp, udp_dscp_v4);
 	ATF_TP_ADD_TC(tp, udp_dscp_v6);
 	ATF_TP_ADD_TC(tp, net_probedscp);
+	ATF_TP_ADD_TC(tp, udp_trunc);
 
 	return (atf_no_error());
 }
diff --git a/lib/isc/unix/socket.c b/lib/isc/unix/socket.c
index 7fe982d493..03226e24ff 100644
--- a/lib/isc/unix/socket.c
+++ b/lib/isc/unix/socket.c
@@ -372,7 +372,7 @@ struct isc__socket {
 				active : 1,         /* currently active */
 				pktdscp : 1;	    /* per packet dscp */
 
-#ifdef ISC_NET_RECVOVERFLOW
+#ifdef ISC_PLATFORM_RECVOVERFLOW
 	unsigned char		overflow; /* used for MSG_TRUNC fake */
 #endif
 
@@ -464,7 +464,7 @@ static isc__socketmgr_t *socketmgr = NULL;
  * send() and recv() iovec counts
  */
 #define MAXSCATTERGATHER_SEND	(ISC_SOCKET_MAXSCATTERGATHER)
-#ifdef ISC_NET_RECVOVERFLOW
+#ifdef ISC_PLATFORM_RECVOVERFLOW
 # define MAXSCATTERGATHER_RECV	(ISC_SOCKET_MAXSCATTERGATHER + 1)
 #else
 # define MAXSCATTERGATHER_RECV	(ISC_SOCKET_MAXSCATTERGATHER)
@@ -1700,10 +1700,6 @@ build_msghdr_recv(isc__socket_t *sock, isc_socketevent_t *dev,
 #else
 		msg->msg_name = (void *)&dev->address.type.sa;
 		msg->msg_namelen = sizeof(dev->address.type);
-#endif
-#ifdef ISC_NET_RECVOVERFLOW
-		/* If needed, steal one iovec for overflow detection. */
-		maxiov--;
 #endif
 	} else { /* TCP */
 		msg->msg_name = NULL;
@@ -1755,12 +1751,11 @@ build_msghdr_recv(isc__socket_t *sock, isc_socketevent_t *dev,
  config:
 
 	/*
-	 * If needed, set up to receive that one extra byte.  Note that
-	 * we know there is at least one iov left, since we stole it
-	 * at the top of this function.
+	 * If needed, set up to receive that one extra byte.
 	 */
-#ifdef ISC_NET_RECVOVERFLOW
+#ifdef ISC_PLATFORM_RECVOVERFLOW
 	if (sock->type == isc_sockettype_udp) {
+		INSIST(iovcount < MAXSCATTERGATHER_RECV);
 		iov[iovcount].iov_base = (void *)(&sock->overflow);
 		iov[iovcount].iov_len = 1;
 		iovcount++;
@@ -1997,7 +1992,7 @@ doio_recv(isc__socket_t *sock, isc_socketevent_t *dev) {
 	 * this indicates an overflow situation.  Set the flag in the
 	 * dev entry and adjust how much we read by one.
 	 */
-#ifdef ISC_NET_RECVOVERFLOW
+#ifdef ISC_PLATFORM_RECVOVERFLOW
 	if ((sock->type == isc_sockettype_udp) && ((size_t)cc > read_count)) {
 		dev->attributes |= ISC_SOCKEVENTATTR_TRUNC;
 		cc--;