diff --git a/irc/channel.go b/irc/channel.go
index f862a844..a6755d22 100644
--- a/irc/channel.go
+++ b/irc/channel.go
@@ -11,6 +11,8 @@ import (
 	"strconv"
 	"time"
 
+	"sync"
+
 	"github.com/DanielOaks/girc-go/ircmsg"
 )
 
@@ -18,6 +20,7 @@ type Channel struct {
 	flags          ChannelModeSet
 	lists          map[ChannelMode]*UserMaskSet
 	key            string
+	membersMutex   sync.RWMutex
 	members        MemberSet
 	name           string
 	nameCasefolded string
@@ -63,6 +66,8 @@ func NewChannel(s *Server, name string, addDefaultModes bool) *Channel {
 }
 
 func (channel *Channel) IsEmpty() bool {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
 	return len(channel.members) == 0
 }
 
@@ -93,6 +98,9 @@ func (channel *Channel) Names(client *Client) {
 
 // ClientIsAtLeast returns whether the client has at least the given channel privilege.
 func (channel *Channel) ClientIsAtLeast(client *Client, permission ChannelMode) bool {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	// get voice, since it's not a part of ChannelPrivModes
 	if channel.members.HasMode(client, permission) {
 		return true
@@ -134,6 +142,9 @@ func (modes ChannelModeSet) Prefixes(isMultiPrefix bool) string {
 }
 
 func (channel *Channel) Nicks(target *Client) []string {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	isMultiPrefix := (target != nil) && target.capabilities[MultiPrefix]
 	isUserhostInNames := (target != nil) && target.capabilities[UserhostInNames]
 	nicks := make([]string, len(channel.members))
@@ -160,7 +171,9 @@ func (channel *Channel) Nick() string {
 
 // <mode> <mode params>
 func (channel *Channel) ModeString(client *Client) (str string) {
+	channel.membersMutex.RLock()
 	isMember := client.flags[Operator] || channel.members.Has(client)
+	channel.membersMutex.RUnlock()
 	showKey := isMember && (channel.key != "")
 	showUserLimit := channel.userLimit > 0
 
@@ -192,6 +205,9 @@ func (channel *Channel) ModeString(client *Client) (str string) {
 }
 
 func (channel *Channel) IsFull() bool {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	return (channel.userLimit > 0) &&
 		(uint64(len(channel.members)) >= channel.userLimit)
 }
@@ -201,6 +217,9 @@ func (channel *Channel) CheckKey(key string) bool {
 }
 
 func (channel *Channel) Join(client *Client, key string) {
+	channel.membersMutex.Lock()
+	defer channel.membersMutex.Unlock()
+
 	if channel.members.Has(client) {
 		// already joined, no message?
 		return
@@ -256,6 +275,9 @@ func (channel *Channel) Join(client *Client, key string) {
 }
 
 func (channel *Channel) Part(client *Client, message string) {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	if !channel.members.Has(client) {
 		client.Send(nil, client.server.name, ERR_NOTONCHANNEL, channel.name, "You're not on that channel")
 		return
@@ -268,6 +290,9 @@ func (channel *Channel) Part(client *Client, message string) {
 }
 
 func (channel *Channel) GetTopic(client *Client) {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	if !channel.members.Has(client) {
 		client.Send(nil, client.server.name, ERR_NOTONCHANNEL, client.nick, channel.name, "You're not on that channel")
 		return
@@ -283,6 +308,9 @@ func (channel *Channel) GetTopic(client *Client) {
 }
 
 func (channel *Channel) SetTopic(client *Client, topic string) {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	if !(client.flags[Operator] || channel.members.Has(client)) {
 		client.Send(nil, client.server.name, ERR_NOTONCHANNEL, channel.name, "You're not on that channel")
 		return
@@ -307,6 +335,9 @@ func (channel *Channel) SetTopic(client *Client, topic string) {
 }
 
 func (channel *Channel) CanSpeak(client *Client) bool {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	if client.flags[Operator] {
 		return true
 	}
@@ -335,6 +366,10 @@ func (channel *Channel) sendMessage(cmd string, minPrefix *ChannelMode, clientOn
 		client.Send(nil, client.server.name, ERR_CANNOTSENDTOCHAN, channel.name, "Cannot send to channel")
 		return
 	}
+
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	// for STATUSMSG
 	var minPrefixMode ChannelMode
 	if minPrefix != nil {
@@ -383,6 +418,9 @@ func (channel *Channel) applyModeFlag(client *Client, mode ChannelMode,
 
 func (channel *Channel) applyModeMember(client *Client, mode ChannelMode,
 	op ModeOp, nick string) *ChannelModeChange {
+	channel.membersMutex.Lock()
+	defer channel.membersMutex.Unlock()
+
 	if nick == "" {
 		//TODO(dan): shouldn't this be handled before it reaches this function?
 		client.Send(nil, client.server.name, ERR_NEEDMOREPARAMS, "MODE", "Not enough parameters")
@@ -466,6 +504,9 @@ func (channel *Channel) applyModeMask(client *Client, mode ChannelMode, op ModeO
 }
 
 func (channel *Channel) Quit(client *Client) {
+	channel.membersMutex.Lock()
+	defer channel.membersMutex.Unlock()
+
 	channel.members.Remove(client)
 	client.channels.Remove(channel)
 
@@ -475,6 +516,9 @@ func (channel *Channel) Quit(client *Client) {
 }
 
 func (channel *Channel) Kick(client *Client, target *Client, comment string) {
+	channel.membersMutex.Lock()
+	defer channel.membersMutex.Unlock()
+
 	if !(client.flags[Operator] || channel.members.Has(client)) {
 		client.Send(nil, client.server.name, ERR_NOTONCHANNEL, channel.name, "You're not on that channel")
 		return
@@ -504,6 +548,9 @@ func (channel *Channel) Invite(invitee *Client, inviter *Client) {
 		return
 	}
 
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	if !channel.members.Has(inviter) {
 		inviter.Send(nil, inviter.server.name, ERR_NOTONCHANNEL, channel.name, "You're not on that channel")
 		return
diff --git a/irc/client.go b/irc/client.go
index fb738b6e..95b0a90a 100644
--- a/irc/client.go
+++ b/irc/client.go
@@ -308,6 +308,8 @@ func (client *Client) Friends(Capabilities ...Capability) ClientSet {
 	}
 
 	for channel := range client.channels {
+		channel.membersMutex.RLock()
+		defer channel.membersMutex.RUnlock()
 		for member := range channel.members {
 			// make sure they have all the required caps
 			for _, Cap := range Capabilities {
diff --git a/irc/modes.go b/irc/modes.go
index 0d29d781..ce8a1ed0 100644
--- a/irc/modes.go
+++ b/irc/modes.go
@@ -345,6 +345,9 @@ func cmodeHandler(server *Server, client *Client, msg ircmsg.IrcMessage) bool {
 	channelName, err := CasefoldChannel(msg.Params[0])
 	channel := server.channels.Get(channelName)
 
+	channel.membersMutex.Lock()
+	defer channel.membersMutex.Unlock()
+
 	if err != nil || channel == nil {
 		client.Send(nil, server.name, ERR_NOSUCHCHANNEL, client.nick, msg.Params[0], "No such channel")
 		return false
diff --git a/irc/roleplay.go b/irc/roleplay.go
index c23dc8d6..a3ec71bd 100644
--- a/irc/roleplay.go
+++ b/irc/roleplay.go
@@ -87,12 +87,14 @@ func sendRoleplayMessage(server *Server, client *Client, source string, targetSt
 			return
 		}
 
+		channel.membersMutex.RLock()
 		for member := range channel.members {
 			if member == client && !client.capabilities[EchoMessage] {
 				continue
 			}
 			member.Send(nil, source, "PRIVMSG", channel.name, message)
 		}
+		channel.membersMutex.RUnlock()
 	} else {
 		target, err := CasefoldName(targetString)
 		user := server.clients.Get(target)
diff --git a/irc/server.go b/irc/server.go
index d472a454..fc1655a0 100644
--- a/irc/server.go
+++ b/irc/server.go
@@ -843,6 +843,9 @@ func (client *Client) WhoisChannelsNames(target *Client) []string {
 	var chstrs []string
 	index := 0
 	for channel := range client.channels {
+		channel.membersMutex.RLock()
+		defer channel.membersMutex.RUnlock()
+
 		// channel is secret and the target can't see it
 		if !target.flags[Operator] && channel.flags[Secret] && !channel.members.Has(target) {
 			continue
@@ -933,6 +936,9 @@ func (target *Client) RplWhoReply(channel *Channel, client *Client) {
 	}
 
 	if channel != nil {
+		channel.membersMutex.RLock()
+		defer channel.membersMutex.RUnlock()
+
 		flags += channel.members[client].Prefixes(target.capabilities[MultiPrefix])
 		channelName = channel.name
 	}
@@ -940,6 +946,9 @@ func (target *Client) RplWhoReply(channel *Channel, client *Client) {
 }
 
 func whoChannel(client *Client, channel *Channel, friends ClientSet) {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	for member := range channel.members {
 		if !client.flags[Invisible] || friends[client] {
 			client.RplWhoReply(channel, member)
@@ -1372,6 +1381,9 @@ func kickHandler(server *Server, client *Client, msg ircmsg.IrcMessage) bool {
 		// make sure client has privs to kick the given user
 		//TODO(dan): split this into a separate function that checks if users have privs
 		// over other users, useful for things like -aoh as well
+		channel.membersMutex.RLock()
+		defer channel.membersMutex.RUnlock()
+
 		var hasPrivs bool
 		for _, mode := range ChannelPrivModes {
 			if channel.members[client][mode] {
@@ -1448,6 +1460,9 @@ func listHandler(server *Server, client *Client, msg ircmsg.IrcMessage) bool {
 }
 
 func (target *Client) RplList(channel *Channel) {
+	channel.membersMutex.RLock()
+	defer channel.membersMutex.RUnlock()
+
 	// get the correct number of channel members
 	var memberCount int
 	if target.flags[Operator] || channel.members.Has(target) {