diff --git a/conn.go b/conn.go
index 04b12371..f3b9bb21 100644
--- a/conn.go
+++ b/conn.go
@@ -1,6 +1,8 @@
 package soju
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"fmt"
 	"io"
@@ -10,6 +12,7 @@ import (
 	"time"
 	"unicode"
 
+	"github.com/DataDog/zstd"
 	"golang.org/x/time/rate"
 	"gopkg.in/irc.v3"
 	"nhooyr.io/websocket"
@@ -25,14 +28,16 @@ type ircConn interface {
 	SetWriteDeadline(time.Time) error
 	RemoteAddr() net.Addr
 	LocalAddr() net.Addr
+	SupportsCompression() bool
+	EnableReadCompression() error
+	EnableWriteCompression() error
 }
 
 func newNetIRCConn(c net.Conn) ircConn {
-	type netConn net.Conn
-	return struct {
-		*irc.Conn
-		netConn
-	}{irc.NewConn(c), c}
+	return &tcpIRCConn{
+		Conn: c,
+		r:    bufio.NewReader(c),
+	}
 }
 
 type websocketIRCConn struct {
@@ -109,6 +114,18 @@ func (wic *websocketIRCConn) LocalAddr() net.Addr {
 	return websocketAddr("")
 }
 
+func (wic websocketIRCConn) SupportsCompression() bool {
+	return false
+}
+
+func (wic websocketIRCConn) EnableReadCompression() error {
+	return fmt.Errorf("websocket: compression is unsupported")
+}
+
+func (wic websocketIRCConn) EnableWriteCompression() error {
+	return fmt.Errorf("websocket: compression is unsupported")
+}
+
 type websocketAddr string
 
 func (websocketAddr) Network() string {
@@ -119,6 +136,74 @@ func (wa websocketAddr) String() string {
 	return string(wa)
 }
 
+type tcpIRCConn struct {
+	net.Conn
+	wz *zstd.Writer
+	rz io.ReadCloser
+	r  *bufio.Reader
+}
+
+func (tic *tcpIRCConn) ReadMessage() (msg *irc.Message, err error) {
+	err = irc.ErrZeroLengthMessage
+	for err == irc.ErrZeroLengthMessage {
+		var line string
+		line, err = tic.r.ReadString('\n')
+		if err != nil {
+			return nil, err
+		}
+		msg, err = irc.ParseMessage(line)
+	}
+	return msg, err
+}
+
+func (tic *tcpIRCConn) WriteMessage(msg *irc.Message) error {
+	data := []byte(msg.String() + "\r\n")
+	if tic.wz != nil {
+		_, err := tic.wz.Write(data)
+		if err != nil {
+			return err
+		}
+		return tic.wz.Flush()
+	}
+	_, err := tic.Conn.Write(data)
+	return err
+}
+
+func (tic *tcpIRCConn) Close() error {
+	if tic.wz != nil {
+		tic.wz.Close()
+	}
+	if tic.rz != nil {
+		tic.rz.Close()
+	}
+	return tic.Conn.Close()
+}
+
+func (tic *tcpIRCConn) SupportsCompression() bool {
+	return true
+}
+
+func (tic *tcpIRCConn) EnableReadCompression() error {
+	if tic.rz == nil {
+		tic.rz = zstd.NewReader(tic)
+		rem, err := tic.r.Peek(tic.r.Buffered())
+		if err != nil {
+			return err
+		}
+		remRd := bytes.NewReader(rem)
+		mr := io.MultiReader(remRd, tic.rz)
+		tic.r = bufio.NewReader(mr)
+	}
+	return nil
+}
+
+func (tic *tcpIRCConn) EnableWriteCompression() error {
+	if tic.wz == nil {
+		tic.wz = zstd.NewWriterLevel(tic, 1)
+	}
+	return nil
+}
+
 type connOptions struct {
 	Logger         Logger
 	RateLimitDelay time.Duration
@@ -162,6 +247,12 @@ func newConn(srv *Server, ic ircConn, options *connOptions) *conn {
 				c.logger.Printf("failed to write message: %v", err)
 				break
 			}
+			if msg.Command == "COMPRESS" {
+				if err := c.conn.EnableWriteCompression(); err != nil {
+					c.logger.Printf("failed to enable compression: %v", err)
+					break
+				}
+			}
 		}
 		if err := c.conn.Close(); err != nil && !isErrClosed(err) {
 			c.logger.Printf("failed to close connection: %v", err)
@@ -207,6 +298,11 @@ func (c *conn) ReadMessage() (*irc.Message, error) {
 	} else if err != nil {
 		return nil, err
 	}
+	if msg.Command == "COMPRESS" && c.conn.SupportsCompression() {
+		if err := c.conn.EnableReadCompression(); err != nil {
+			return nil, err
+		}
+	}
 
 	c.logger.Debugf("received: %v", msg)
 	return msg, nil
diff --git a/downstream.go b/downstream.go
index 30ef902f..b454c3fa 100644
--- a/downstream.go
+++ b/downstream.go
@@ -337,6 +337,9 @@ func newDownstreamConn(srv *Server, ic ircConn, id uint64) *downstreamConn {
 	if srv.Config().LogPath != "" {
 		dc.supportedCaps["draft/chathistory"] = ""
 	}
+	if dc.conn.conn.SupportsCompression() {
+		dc.supportedCaps["draft/compression"] = ""
+	}
 	return dc
 }
 
@@ -796,11 +799,23 @@ func (dc *downstreamConn) handleMessageUnregistered(ctx context.Context, msg *ir
 
 			dc.networkName = match.GetName()
 		}
+	case "COMPRESS":
+		// handled in dc.conn.ReadMessage() if supported
+		if !dc.conn.conn.SupportsCompression() {
+			return newUnknownCommandError(msg.Command)
+		}
 	default:
 		dc.logger.Printf("unhandled message: %v", msg)
 		return newUnknownCommandError(msg.Command)
 	}
 	if dc.rawUsername != "" && dc.nick != "*" && !dc.negotiatingCaps {
+		if dc.caps["draft/compression"] {
+			// triggers compression at dc.conn level
+			dc.SendMessage(&irc.Message{
+				Prefix:  dc.srv.prefix(),
+				Command: "COMPRESS",
+			})
+		}
 		return dc.register(ctx)
 	}
 	return nil
@@ -2843,6 +2858,11 @@ func (dc *downstreamConn) handleMessageRegistered(ctx context.Context, msg *irc.
 				})
 			}
 		})
+	case "COMPRESS":
+		// handled in dc.conn.ReadMessage() if supported
+		if !dc.conn.conn.SupportsCompression() {
+			return newUnknownCommandError(msg.Command)
+		}
 	case "BOUNCER":
 		var subcommand string
 		if err := parseMessageParams(msg, &subcommand); err != nil {
diff --git a/go.mod b/go.mod
index 462a98bf..ab9c4a02 100644
--- a/go.mod
+++ b/go.mod
@@ -5,6 +5,7 @@ go 1.15
 require (
 	git.sr.ht/~emersion/go-scfg v0.0.0-20201019143924-142a8aa629fc
 	git.sr.ht/~sircmpwn/go-bare v0.0.0-20210406120253-ab86bc2846d9
+	github.com/DataDog/zstd v1.5.0
 	github.com/cespare/xxhash/v2 v2.1.2 // indirect
 	github.com/emersion/go-sasl v0.0.0-20211008083017-0b9dcfb154ac
 	github.com/golang/protobuf v1.5.2 // indirect
diff --git a/go.sum b/go.sum
index 8c11e230..f5bbf08a 100644
--- a/go.sum
+++ b/go.sum
@@ -38,6 +38,8 @@ git.sr.ht/~sircmpwn/go-bare v0.0.0-20210406120253-ab86bc2846d9 h1:Ahny8Ud1LjVMMA
 git.sr.ht/~sircmpwn/go-bare v0.0.0-20210406120253-ab86bc2846d9/go.mod h1:BVJwbDfVjCjoFiKrhkei6NdGcZYpkDkdyCdg1ukytRA=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
+github.com/DataDog/zstd v1.5.0 h1:+K/VEwIAaPcHiMtQvpLD4lqW7f0Gk3xdYZmI1hD+CXo=
+github.com/DataDog/zstd v1.5.0/go.mod h1:g4AWEaM3yOg3HYfnJ3YIawPnVdXJh9QME85blwSAmyw=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/template v0.0.0-20190718012654-fb15b899a751/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=