diff --git a/master/src/master_server.rs b/master/src/master_server.rs
index 034470b..d6d8ad4 100644
--- a/master/src/master_server.rs
+++ b/master/src/master_server.rs
@@ -9,6 +9,7 @@ use std::{
     io,
     net::{Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6, ToSocketAddrs, UdpSocket},
     ops::Deref,
+    str::FromStr,
     sync::atomic::{AtomicBool, Ordering},
     time::{Duration, Instant},
 };
@@ -35,7 +36,7 @@ use crate::{
 };
 
 pub trait AddrExt: Sized + Eq + Hash + Display + Copy + ToSocketAddrs + ServerAddress {
-    type Ip;
+    type Ip: Eq + Hash + Display + Copy + FromStr;
 
     fn extract(addr: SocketAddr) -> Result<Self, SocketAddr>;
     fn ip(&self) -> &Self::Ip;
@@ -261,11 +262,7 @@ impl Master {
     }
 }
 
-impl<Addr> MasterServer<Addr>
-where
-    Addr: AddrExt,
-    Addr::Ip: Eq + Hash + Display + Copy + std::str::FromStr,
-{
+impl<Addr: AddrExt> MasterServer<Addr> {
     pub fn new(cfg: Config, addr: Addr) -> Result<Self, Error> {
         info!("Listen address: {}", addr);
 
@@ -694,7 +691,6 @@ where
         fn helper<Addr, F>(args: &[&str], mut op: F)
         where
             Addr: AddrExt,
-            Addr::Ip: std::str::FromStr,
             F: FnMut(&str, Addr::Ip),
         {
             let iter = args.iter().map(|i| (i, i.parse::<Addr::Ip>()));