diff --git a/src/iperf.h b/src/iperf.h
index 55ad513..ffbd6d3 100644
--- a/src/iperf.h
+++ b/src/iperf.h
@@ -62,6 +62,7 @@ struct iperf_settings
     int       mss;                  /* for TCP MSS */
     int       ttl;                  /* IP TTL option */
     int       tos;                  /* type of service bit */
+    int       flowlabel;            /* IPv6 flow label */
     iperf_size_t bytes;             /* number of bytes to send */
     char      unit_format;          /* -f */
 };
diff --git a/src/iperf3.1 b/src/iperf3.1
index ab20419..d32874b 100644
--- a/src/iperf3.1
+++ b/src/iperf3.1
@@ -94,6 +94,9 @@ only use IPv6
 .TP
 .BR -S ", " --tos " \fIn\fR"
 set the IP 'type of service'
+.\" .TP
+.\" .BR -L ", " --flowlabel " \fIn\fR"
+.\" set the IPv6 'flow label'
 .TP
 .BR -Z ", " --zerocopy " "
 Use a "zero copy" method of sending data, such as sendfile(2),
diff --git a/src/iperf_api.c b/src/iperf_api.c
index 7615c2d..e37fb85 100644
--- a/src/iperf_api.c
+++ b/src/iperf_api.c
@@ -430,14 +430,14 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
         {"no-delay", no_argument, NULL, 'N'},
         {"version6", no_argument, NULL, '6'},
         {"tos", required_argument, NULL, 'S'},
+        {"flowlabel", required_argument, NULL, 'L'},
         {"zerocopy", no_argument, NULL, 'Z'},
         {"help", no_argument, NULL, 'h'},
 
-    /*  XXX: The following ifdef needs to be split up. linux-congestion is not necessarily supported
-     *  by systems that support tos.
+    /*  XXX: The following ifdef needs to be split up. linux-congestion is not
+     * necessarily supported by systems that support tos.
      */
 #ifdef ADD_WHEN_SUPPORTED
-        {"tos",        required_argument, NULL, 'S'},
         {"linux-congestion", required_argument, NULL, 'L'},
 #endif
         {NULL, 0, NULL, 0}
@@ -448,7 +448,7 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
 
     blksize = 0;
     server_flag = client_flag = 0;
-    while ((flag = getopt_long(argc, argv, "p:f:i:DVJdvsc:ub:t:n:l:P:Rw:B:M:N46S:Zh", longopts, NULL)) != -1) {
+    while ((flag = getopt_long(argc, argv, "p:f:i:DVJdvsc:ub:t:n:l:P:Rw:B:M:N46S:L:Zh", longopts, NULL)) != -1) {
         switch (flag) {
             case 'p':
                 test->server_port = atoi(optarg);
@@ -569,10 +569,22 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
                 test->settings->domain = AF_INET6;
                 break;
             case 'S':
-                // XXX: Checking for errors in strtol is not portable. Leave as is?
                 test->settings->tos = strtol(optarg, NULL, 0);
 		client_flag = 1;
                 break;
+            case 'L':
+#ifdef notdef
+                test->settings->flowlabel = strtol(optarg, NULL, 0);
+		if (test->settings->flowlabel < 1 || test->settings->flowlabel > 0xfffff) {
+                    i_errno = IESETFLOW;
+                    return -1;
+		}
+		client_flag = 1;
+#else /* notdef */
+		i_errno = IEUNIMP;
+		return -1;
+#endif /* notdef */
+                break;
             case 'Z':
                 if (!has_sendfile()) {
                     i_errno = IENOSENDFILE;
@@ -889,6 +901,8 @@ send_parameters(struct iperf_test *test)
 	    cJSON_AddIntToObject(j, "bandwidth", test->settings->rate);
 	if (test->settings->tos)
 	    cJSON_AddIntToObject(j, "TOS", test->settings->tos);
+	if (test->settings->flowlabel)
+	    cJSON_AddIntToObject(j, "flowlabel", test->settings->flowlabel);
 	if (JSON_write(test->ctrl_sck, j) < 0) {
 	    i_errno = IESENDPARAMS;
 	    r = -1;
@@ -938,6 +952,8 @@ get_parameters(struct iperf_test *test)
 	    test->settings->rate = j_p->valueint;
 	if ((j_p = cJSON_GetObjectItem(j, "TOS")) != NULL)
 	    test->settings->tos = j_p->valueint;
+	if ((j_p = cJSON_GetObjectItem(j, "flowlabel")) != NULL)
+	    test->settings->flowlabel = j_p->valueint;
 	if (test->sender && test->protocol->id == Ptcp && has_tcpinfo_retransmits())
 	    test->sender_has_retransmits = 1;
 	cJSON_Delete(j);
@@ -1832,6 +1848,7 @@ iperf_init_stream(struct iperf_stream *sp, struct iperf_test *test)
         i_errno = IEINITSTREAM;
         return -1;
     }
+
     /* Set IP TOS */
     if ((opt = test->settings->tos)) {
         if (getsockdomain(sp->socket) == AF_INET6) {
diff --git a/src/iperf_api.h b/src/iperf_api.h
index 8936d8c..418eebc 100644
--- a/src/iperf_api.h
+++ b/src/iperf_api.h
@@ -222,6 +222,7 @@ enum {
     IEINTERVAL = 9,         // Report interval too large. Maxumum value = %dMAX_INTERVAL
     IEMSS = 10,             // MSS too large. Maximum value = %dMAX_MSS
     IENOSENDFILE = 11,      // This OS does not support sendfile
+    IEUNIMP = 12,           // Not implemented yet
     /* Test errors */
     IENEWTEST = 100,        // Unable to create a new test (check perror)
     IEINITTEST = 101,       // Test initialization failed (check perror)
@@ -250,10 +251,11 @@ enum {
     IESETBUF = 124,         // Unable to set socket buffer size (check perror)
     IESETTOS = 125,         // Unable to set IP TOS (check perror)
     IESETCOS = 126,         // Unable to set IPv6 traffic class (check perror)
-    IEREUSEADDR = 127,      // Unable to set reuse address on socket (check perror)
-    IENONBLOCKING = 128,    // Unable to set socket to non-blocking (check perror)
-    IESETWINDOWSIZE = 129,  // Unable to set socket window size (check perror)
-    IEPROTOCOL = 130,       // Protocol does not exist
+    IESETFLOW = 127,        // Unable to set IPv6 flow label
+    IEREUSEADDR = 128,      // Unable to set reuse address on socket (check perror)
+    IENONBLOCKING = 129,    // Unable to set socket to non-blocking (check perror)
+    IESETWINDOWSIZE = 130,  // Unable to set socket window size (check perror)
+    IEPROTOCOL = 131,       // Protocol does not exist
     /* Stream errors */
     IECREATESTREAM = 200,   // Unable to create a new stream (check herror/perror)
     IEINITSTREAM = 201,     // Unable to initialize stream (check herror/perror)
diff --git a/src/iperf_error.c b/src/iperf_error.c
index d8c8010..c5d9910 100644
--- a/src/iperf_error.c
+++ b/src/iperf_error.c
@@ -99,6 +99,9 @@ iperf_strerror(int i_errno)
         case IENOSENDFILE:
             snprintf(errstr, len, "this OS does not support sendfile");
             break;
+        case IEUNIMP:
+            snprintf(errstr, len, "an option you are trying to set is not implemented yet");
+            break;
         case IENEWTEST:
             snprintf(errstr, len, "unable to create a new test");
             perr = 1;
@@ -203,6 +206,9 @@ iperf_strerror(int i_errno)
             snprintf(errstr, len, "unable to set IPv6 traffic class");
             perr = 1;
             break;
+        case IESETFLOW:
+            snprintf(errstr, len, "unable to set IPv6 flow label");
+            break;
         case IEREUSEADDR:
             snprintf(errstr, len, "unable to reuse address on socket");
             perr = 1;
diff --git a/src/iperf_tcp.c b/src/iperf_tcp.c
index 3165842..b47ebda 100644
--- a/src/iperf_tcp.c
+++ b/src/iperf_tcp.c
@@ -263,6 +263,15 @@ iperf_tcp_connect(struct iperf_test *test)
             return -1;
         }
     }
+    if (test->settings->flowlabel) {
+        if (server_res->ai_addr->sa_family != AF_INET6) {
+            i_errno = IESETFLOW;
+            return -1;
+	} else {
+	    struct sockaddr_in6* sa6P = (struct sockaddr_in6*) server_res->ai_addr;
+	    sa6P->sin6_flowinfo = htonl(test->settings->flowlabel);
+	}
+    }
 
     if (connect(s, (struct sockaddr *) server_res->ai_addr, server_res->ai_addrlen) < 0 && errno != EINPROGRESS) {
         i_errno = IESTREAMCONNECT;
diff --git a/src/locale.c b/src/locale.c
index 40e4fc0..a827625 100644
--- a/src/locale.c
+++ b/src/locale.c
@@ -97,6 +97,7 @@ const char usage_longstr[] = "Usage: iperf [-s|-c host] [options]\n"
                            "  -4, --version4            only use IPv4\n"
                            "  -6, --version6            only use IPv6\n"
                            "  -S, --tos N               set the IP 'type of service'\n"
+                           /* "  -L, --flowlabel N         set the IPv6 'flow label'\n" */
                            "  -Z, --zerocopy            use a 'zero copy' method of sending data\n"
 
 #ifdef NOT_YET_SUPPORTED /* still working on these */