diff --git a/man/opensm.8.in b/man/opensm.8.in

index df557682058f..283483389d20 100644

--- a/man/opensm.8.in

+++ b/man/opensm.8.in

@@ -11,6 +11,7 @@ opensm \- InfiniBand subnet manager and administration (SM/SA)

 [\-g(uid) <GUID in hex>]

 [\-l(mc) <LMC>]

 [\-p(riority) <PRIORITY>]

+[\-\-subnet_prefix <PREFIX in hex>]

 [\-\-smkey <SM_Key>]

 [\-\-sm_sl <SL number>]

 [\-r(eassign_lids)]

@@ -136,6 +137,13 @@ This will effect the handover cases, where master

 is chosen by priority and GUID.  Range goes from 0

 (default and lowest priority) to 15 (highest).

 .TP

+\fB\-\-subnet_prefix\fR <PREFIX in hex>

+This option specifies the subnet prefix to use

+on the fabric.  The default prefix is

+0xfe80000000000000.  OpenMPI in particular requires

+separate fabrics plugged into different ports to

+have different prefixes or else it won't run.

+.TP

 \fB\-\-smkey\fR <SM_Key value>

 This option specifies the SM\'s SM_Key (64 bits).

 This will effect SM authentication.

diff --git a/opensm/main.c b/opensm/main.c

index 2d23fe2befef..b4bb3481cf8f 100644

--- a/opensm/main.c

+++ b/opensm/main.c

@@ -161,6 +161,9 @@ static void show_usage(void)

 	       "          This will effect the handover cases, where master\n"

 	       "          is chosen by priority and GUID.  Range goes\n"

 	       "          from 0 (lowest priority) to 15 (highest).\n\n");

+	printf("--subnet_prefix <prefix>\n"

+	       "          Set the subnet prefix to something other than the\n"

+	       "          default value of 0xfe80000000000000\n\n");

 	printf("--smkey, -k <SM_Key>\n"

 	       "          This option specifies the SM's SM_Key (64 bits).\n"

 	       "          This will effect SM authentication.\n"

@@ -665,6 +668,7 @@ int main(int argc, char *argv[])

 		{"once", 0, NULL, 'o'},

 		{"reassign_lids", 0, NULL, 'r'},

 		{"priority", 1, NULL, 'p'},

+		{"subnet_prefix", 1, NULL, 15},

 		{"smkey", 1, NULL, 'k'},

 		{"routing_engine", 1, NULL, 'R'},

 		{"ucast_cache", 0, NULL, 'A'},

@@ -1008,6 +1012,11 @@ int main(int argc, char *argv[])

 			printf(" Priority = %d\n", temp);

 			break;

+		case 16:

+			opt.subnet_prefix = cl_hton64(strtoull(optarg, NULL, 16));

+			printf(" Subnet_Prefix = <0x%" PRIx64 ">\n", cl_hton64(opt.subnet_prefix));

+			break;

+

 		case 'k':

 			sm_key = cl_hton64(strtoull(optarg, NULL, 16));

 			printf(" SM Key <0x%" PRIx64 ">\n", cl_hton64(sm_key));