diff --git a/DEVELOPING.md b/DEVELOPING.md
index 63aba519..3accd60f 100644
--- a/DEVELOPING.md
+++ b/DEVELOPING.md
@@ -184,3 +184,14 @@ We also support grabbing translations directly from CrowdIn. To do this:
 4. Run `crowdin download`
 
 This will download a bunch of updated files and put them in the right place
+
+
+## Adding a mode
+
+When adding a mode, keep in mind the following places it may need to be referenced:
+
+1. The mode needs to be defined in the `irc/modes` subpackage
+1. It may need to be special-cased in `modes.RplMyInfo()`
+1. It may need to be added to the `CHANMODES` ISUPPORT token
+1. It may need special handling in `ApplyUserModeChanges` or `ApplyChannelModeChanges`
+1. It may need special persistence handling code
diff --git a/irc/config.go b/irc/config.go
index 53d59e16..f169522c 100644
--- a/irc/config.go
+++ b/irc/config.go
@@ -1287,7 +1287,7 @@ func (config *Config) generateISupport() (err error) {
 	isupport.Add("BOT", "B")
 	isupport.Add("CASEMAPPING", "ascii")
 	isupport.Add("CHANLIMIT", fmt.Sprintf("%s:%d", chanTypes, config.Channels.MaxChannelsPerClient))
-	isupport.Add("CHANMODES", strings.Join([]string{modes.Modes{modes.BanMask, modes.ExceptMask, modes.InviteMask}.String(), modes.Modes{modes.Key}.String(), modes.Modes{modes.UserLimit}.String(), modes.Modes{modes.InviteOnly, modes.Moderated, modes.NoOutside, modes.OpOnlyTopic, modes.ChanRoleplaying, modes.Secret, modes.NoCTCP, modes.RegisteredOnly, modes.RegisteredOnlySpeak}.String()}, ","))
+	isupport.Add("CHANMODES", chanmodesToken)
 	if config.History.Enabled && config.History.ChathistoryMax > 0 {
 		isupport.Add("draft/CHATHISTORY", strconv.Itoa(config.History.ChathistoryMax))
 	}
diff --git a/irc/modes/modes.go b/irc/modes/modes.go
index 5fa51109..cf7cc1f2 100644
--- a/irc/modes/modes.go
+++ b/irc/modes/modes.go
@@ -6,6 +6,7 @@
 package modes
 
 import (
+	"fmt"
 	"sort"
 	"strings"
 
@@ -450,3 +451,22 @@ func RplMyInfo() (param1, param2, param3 string) {
 
 	return userModes.String(), channelModes.String(), channelParametrizedModes.String()
 }
+
+func ChanmodesToken() (result string) {
+	// https://modern.ircdocs.horse#chanmodes-parameter
+	// type A: listable modes with parameters
+	A := Modes{BanMask, ExceptMask, InviteMask}
+	// type B: modes with parameters
+	B := Modes{Key}
+	// type C: modes that take a parameter only when set, never when unset
+	C := Modes{UserLimit}
+	// type D: modes without parameters
+	D := Modes{InviteOnly, Moderated, NoOutside, OpOnlyTopic, ChanRoleplaying, Secret, NoCTCP, RegisteredOnly, RegisteredOnlySpeak, Auditorium, OpModerated}
+
+	sort.Sort(ByCodepoint(A))
+	sort.Sort(ByCodepoint(B))
+	sort.Sort(ByCodepoint(C))
+	sort.Sort(ByCodepoint(D))
+
+	return fmt.Sprintf("%s,%s,%s,%s", A.String(), B.String(), C.String(), D.String())
+}
diff --git a/irc/modes/modes_test.go b/irc/modes/modes_test.go
index 858fa836..27f04888 100644
--- a/irc/modes/modes_test.go
+++ b/irc/modes/modes_test.go
@@ -5,6 +5,7 @@ package modes
 
 import (
 	"reflect"
+	"strings"
 	"testing"
 )
 
@@ -219,6 +220,15 @@ func TestHighestChannelUserMode(t *testing.T) {
 	}
 }
 
+func TestChanmodesToken(t *testing.T) {
+	tok := ChanmodesToken()
+	for _, mode := range SupportedChannelModes {
+		if strings.IndexRune(tok, rune(mode)) == -1 {
+			t.Errorf("+%s not included in ChanmodesToken()", mode)
+		}
+	}
+}
+
 func TestModeChangesString(t *testing.T) {
 	m := ModeChanges{
 		ModeChange{Op: Add, Mode: RegisteredOnly},
diff --git a/irc/server.go b/irc/server.go
index 328166f7..9e679e01 100644
--- a/irc/server.go
+++ b/irc/server.go
@@ -39,6 +39,9 @@ var (
 	// three final parameters of 004 RPL_MYINFO, enumerating our supported modes
 	rplMyInfo1, rplMyInfo2, rplMyInfo3 = modes.RplMyInfo()
 
+	// CHANMODES isupport token
+	chanmodesToken = modes.ChanmodesToken()
+
 	// whitelist of caps to serve on the STS-only listener. In particular,
 	// never advertise SASL, to discourage people from sending their passwords:
 	stsOnlyCaps = caps.NewSet(caps.STS, caps.MessageTags, caps.ServerTime, caps.Batch, caps.LabeledResponse, caps.EchoMessage, caps.Nope)