diff --git a/lib/cli.py b/lib/cli.py
index 3c735432d4546a917be1a2bdef67f7dbf3b84bdc..233376060ca1078abed32041a33d7218ef36ce96 100644
--- a/lib/cli.py
+++ b/lib/cli.py
@@ -69,6 +69,7 @@ __all__ = [
   "IGNORE_FAILURES_OPT",
   "IGNORE_SIZE_OPT",
   "FORCE_OPT",
+  "MAC_PREFIX_OPT",
   "MC_OPT",
   "NET_OPT",
   "NEW_SECONDARY_OPT",
@@ -752,6 +753,12 @@ NOVOTING_OPT = cli_option("--no-voting", dest="no_voting",
                           help="Skip node agreement check (dangerous)",
                           action="store_true", default=False)
 
+MAC_PREFIX_OPT = cli_option("-m", "--mac-prefix", dest="mac_prefix",
+                            help="Specify the mac prefix for the instance IP"
+                            " addresses, in the format XX:XX:XX",
+                            metavar="PREFIX",
+                            default=None)
+
 
 def _ParseArgs(argv, commands, aliases):
   """Parser for the command line arguments.
diff --git a/scripts/gnt-cluster b/scripts/gnt-cluster
index e931032b788b42dcda3fb075de2bbc90de21eef1..bf4420243f0c6bec4993e1fc462fcf7b4ff1a051 100755
--- a/scripts/gnt-cluster
+++ b/scripts/gnt-cluster
@@ -84,6 +84,9 @@ def InitCluster(opts, args):
   if opts.candidate_pool_size is None:
     opts.candidate_pool_size = constants.MASTER_POOL_SIZE_DEFAULT
 
+  if opts.mac_prefix is None:
+    opts.mac_prefix = constants.DEFAULT_MAC_PREFIX
+
   bootstrap.InitCluster(cluster_name=args[0],
                         secondary_ip=opts.secondary_ip,
                         vg_name=vg_name,
@@ -595,11 +598,7 @@ commands = {
   'init': (InitCluster, [ArgHost(min=1, max=1)],
            [DEBUG_OPT,
             SECONDARY_IP_OPT,
-            cli_option("-m", "--mac-prefix", dest="mac_prefix",
-                       help="Specify the mac prefix for the instance IP"
-                       " addresses, in the format XX:XX:XX",
-                       metavar="PREFIX",
-                       default=constants.DEFAULT_MAC_PREFIX,),
+            MAC_PREFIX_OPT,
             VG_NAME_OPT,
             cli_option("--master-netdev", dest="master_netdev",
                        help="Specify the node interface (cluster-wide)"