diff --git a/upstream.go b/upstream.go
index e2dd8d6..2d6b4eb 100644
--- a/upstream.go
+++ b/upstream.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"strings"
 
 	"gopkg.in/irc.v3"
 )
@@ -14,12 +15,52 @@ const (
 	rpl_globalusers = "266"
 )
 
+type modeSet string
+
+func (ms modeSet) Has(c byte) bool {
+	return strings.IndexByte(string(ms), c) >= 0
+}
+
+func (ms *modeSet) Add(c byte) {
+	if !ms.Has(c) {
+		*ms += modeSet(c)
+	}
+}
+
+func (ms *modeSet) Del(c byte) {
+	i := strings.IndexByte(string(*ms), c)
+	if i >= 0 {
+		*ms = (*ms)[:i] + (*ms)[i+1:]
+	}
+}
+
+func (ms *modeSet) Apply(s string) error {
+	var plusMinus byte
+	for i := 0; i < len(s); i++ {
+		switch c := s[i]; c {
+		case '+', '-':
+			plusMinus = c
+		default:
+			switch plusMinus {
+			case '+':
+				ms.Add(c)
+			case '-':
+				ms.Del(c)
+			default:
+				return fmt.Errorf("malformed modestring %q: missing plus/minus", s)
+			}
+		}
+	}
+	return nil
+}
+
 type upstreamConn struct {
 	upstream   *Upstream
 	net        net.Conn
 	irc        *irc.Conn
 	srv        *Server
 	registered bool
+	modes      modeSet
 
 	serverName            string
 	availableUserModes    string
@@ -35,6 +76,14 @@ func (c *upstreamConn) handleMessage(msg *irc.Message) error {
 			Command: "PONG",
 			Params:  []string{c.srv.Hostname},
 		})
+	case "MODE":
+		if len(msg.Params) < 2 {
+			return newNeedMoreParamsError(msg.Command)
+		}
+		if nick := msg.Params[0]; nick != c.upstream.Nick {
+			return fmt.Errorf("received MODE message for unknow nick %q", nick)
+		}
+		return c.modes.Apply(msg.Params[1])
 	case irc.RPL_WELCOME:
 		c.registered = true
 		c.srv.Logger.Printf("Connection to %q registered", c.upstream.Addr)