diff --git a/irc/channel.go b/irc/channel.go
index 54d9d286..7f2c455d 100644
--- a/irc/channel.go
+++ b/irc/channel.go
@@ -2,6 +2,7 @@ package irc
 
 import (
 	"log"
+	"sync"
 )
 
 type Channel struct {
@@ -10,6 +11,7 @@ type Channel struct {
 	destroyed bool
 	key       string
 	members   ClientSet
+	mutex     *sync.Mutex
 	name      string
 	noOutside bool
 	password  string
@@ -38,6 +40,7 @@ func NewChannel(s *Server, name string) *Channel {
 		banList:  make([]UserMask, 0),
 		commands: commands,
 		members:  make(ClientSet),
+		mutex:    &sync.Mutex{},
 		name:     name,
 		replies:  replies,
 		server:   s,
@@ -92,11 +95,13 @@ func (channel *Channel) receiveReplies(replies <-chan Reply) {
 		if DEBUG_CHANNEL {
 			log.Printf("%s ← %s %s", channel, reply.Source(), reply)
 		}
+		channel.mutex.Lock()
 		for client := range channel.members {
 			if reply.Source() != Identifier(client) {
 				client.Reply(reply)
 			}
 		}
+		channel.mutex.Unlock()
 	}
 }
 
diff --git a/irc/server.go b/irc/server.go
index a0a5db68..027f5436 100644
--- a/irc/server.go
+++ b/irc/server.go
@@ -9,6 +9,7 @@ import (
 	"log"
 	"net"
 	"os"
+	"sync"
 	"time"
 )
 
@@ -17,6 +18,7 @@ type Server struct {
 	commands  chan Command
 	ctime     time.Time
 	motdFile  string
+	mutex     *sync.Mutex
 	name      string
 	operators map[string]string
 	password  string
@@ -30,6 +32,7 @@ func NewServer(config *Config) *Server {
 		commands:  make(chan Command),
 		ctime:     time.Now(),
 		motdFile:  config.MOTD,
+		mutex:     &sync.Mutex{},
 		name:      config.Name,
 		operators: make(map[string]string),
 		password:  config.Password,
@@ -296,7 +299,9 @@ func (m *QuitCommand) HandleServer(server *Server) {
 	iclients.Remove(client)
 
 	for channel := range client.channels {
+		channel.mutex.Lock()
 		channel.members.Remove(client)
+		channel.mutex.Unlock()
 	}
 
 	client.Reply(RplError(server, client))