diff --git a/Main.hs b/Main.hs
--- a/Main.hs
+++ b/Main.hs
@@ -4,56 +4,79 @@
 -- License    : BSD-Style
 -- Maintainer : michel.boucey@gmail.com
 --
--- commandline tool to generate IPv6 address text representations
+-- Commandline tool to generate IPv6 address text representations
 --
 -- -----------------------------------------------------------------------------
 
 {-# LANGUAGE DeriveDataTypeable,OverloadedStrings #-}
 
-import Control.Applicative ((<$>))
 import Control.Monad (replicateM_)
 import Data.Text as T (append,pack)
 import Data.Text.IO as TIO (putStrLn,hPutStrLn)
 import System.Console.CmdArgs
 import System.Exit
 import System.IO (stderr)
+
 import Text.IPv6Addr
 
 data Input =Input
     { output   :: String
     , address  :: String
     , quantity :: Int
+    , prefix   :: String
     } deriving (Show,Data,Typeable)
 
 ip6addrInput :: Input
 ip6addrInput = Input
-    { address = "" &= typ " <IPv6 address>"
-    , output = "canonical" &= typ " [pure|canonical|full|arpa|random]" &= help "(default=canonical)"
-    , quantity = 1 &= help "Amount of random addresses to generate" &= typ " <Integer>"
-    } &= summary "ip6addr version 0.4 (C) Michel Boucey 2015"
+    { address = ""
+      &= typ " <IPv6 address>"
+    , output = "canonical"
+      &= typ " [pure|canonical|full|arpa|random]"
+      &= help "(default=canonical)"
+    , quantity = 1
+      &= help "Amount of random addresses to generate"
+      &= typ " <Integer>"
+    , prefix = ""
+      &= typ " <Prefix>"
+      &= help "Set a prefix for random addresses generation"
+    } &= summary "ip6addr version 0.5 (C) Michel Boucey 2015"
       &= program "ip6addr"
       &= helpArg [name "h"]
-      &= details ["Examples:","  ip6addr -a 0:0::FFFF:192.0.2.128","  ip6addr -o full -a ::1","  ip6addr -o random -q 10",""]
+      &= details [ "Examples:"
+                 , ""
+                 , "  ip6addr -a 0:0::FFFF:192.0.2.128"
+                 , "  ip6addr -o full -a ::1"
+                 , "  ip6addr -o random -q 10 -p 1234:abcd::"
+                 , ""
+                 ]
 
 main :: IO ()
 main = do
     a <- cmdArgs ip6addrInput
     if output a == "random"
-        then replicateM_ (quantity a) putRandAddr >> exitSuccess
-        else do let m = address a
-                case output a of
-                    "canonical" -> out maybeIPv6Addr m fromIPv6Addr
-                    "full"      -> out maybeFullIPv6Addr m fromIPv6Addr
-                    "arpa"      -> out maybePureIPv6Addr m toIP6ARPA
-                    "pure"      -> out maybePureIPv6Addr m fromIPv6Addr
-                    _           -> hPutStrLn stderr "See help"
-                                >> exitFailure
+        then replicateM_ (quantity a) (putRandAddr (prefix a)) >> exitSuccess
+        else do
+            let m = address a
+            case output a of
+                "canonical" -> out maybeIPv6Addr m fromIPv6Addr
+                "full"      -> out maybeFullIPv6Addr m fromIPv6Addr
+                "arpa"      -> out maybePureIPv6Addr m toIP6ARPA
+                "pure"      -> out maybePureIPv6Addr m fromIPv6Addr
+                _           -> hPutStrLn stderr "See help" >> exitFailure
   where
-    putRandAddr = fromIPv6Addr <$> randIPv6Addr >>= TIO.putStrLn
+    putRandAddr p = do
+        r <- randIPv6AddrWithPrefix $
+                 if p == "" then Nothing else Just $ T.pack p
+        case r of
+            Nothing -> TIO.putStrLn "Bad prefix"
+            Just a  -> TIO.putStrLn $ fromIPv6Addr a
     out t i o =
         if i /= ""
-            then do let p = T.pack i
-                    case t p of
-                        Nothing -> hPutStrLn stderr ("'" `T.append` p `T.append` "' is not an IPv6 address") >> exitFailure
-                        Just a  -> TIO.putStrLn (o a) >> exitSuccess
+            then do
+                let p = T.pack i
+                case t p of
+                    Nothing -> hPutStrLn stderr 
+                        ("'" `T.append` p `T.append` "' is not an IPv6 address")
+                        >> exitFailure
+                    Just a  -> TIO.putStrLn (o a) >> exitSuccess
             else Prelude.putStrLn "See help" >> exitFailure
diff --git a/ip6addr.cabal b/ip6addr.cabal
--- a/ip6addr.cabal
+++ b/ip6addr.cabal
@@ -1,7 +1,7 @@
 name:                ip6addr
-version:             0.4.0.0
-synopsis:            commandline tool to generate IPv6 address text representations
-description:         commandline tool to generate IPv6 address text representations
+version:             0.5.0.0
+synopsis:            Commandline tool to generate IPv6 address text representations
+description:         Commandline tool to generate IPv6 address text representations
 license:             BSD3
 license-file:        LICENSE
 author:              Michel Boucey
@@ -17,8 +17,8 @@
   Location: https://github.com/MichelBoucey/ip6addr.git
 
 executable ip6addr
-  GHC-Options: -O2 -Wall
+  GHC-Options: -Wall
   main-is:             Main.hs
   other-extensions:    DeriveDataTypeable, OverloadedStrings
-  build-depends:       base >=4.7 && <4.8, cmdargs,IPv6Addr >= 0.5, text >= 1.2
+  build-depends:       base >=4.7 && <4.8, cmdargs,IPv6Addr >= 0.6, text >= 1.2
   default-language:    Haskell2010