diff --git a/.travis.yml b/.travis.yml
index b2a5629..a2db8b6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -19,6 +19,7 @@ install:
 
 before_script:
   - docker-compose up -d
+  - echo 'replace github.com/at-wat/mqtt-go => ../' >> paho/go.mod
 
 script:
   - go vet -tags integration ./...
diff --git a/client.go b/client.go
index 712cabc..f47d8c3 100644
--- a/client.go
+++ b/client.go
@@ -30,39 +30,6 @@ func (c *BaseClient) Handle(handler Handler) {
 	c.handler = handler
 }
 
-// WithUserNamePassword sets plain text auth information used in Connect.
-func WithUserNamePassword(userName, password string) ConnectOption {
-	return func(o *ConnectOptions) error {
-		o.UserName = userName
-		o.Password = password
-		return nil
-	}
-}
-
-// WithKeepAlive sets keep alive interval in seconds.
-func WithKeepAlive(interval uint16) ConnectOption {
-	return func(o *ConnectOptions) error {
-		o.KeepAlive = interval
-		return nil
-	}
-}
-
-// WithCleanSession sets clean session flag.
-func WithCleanSession(cleanSession bool) ConnectOption {
-	return func(o *ConnectOptions) error {
-		o.CleanSession = cleanSession
-		return nil
-	}
-}
-
-// WithWill sets will message.
-func WithWill(will *Message) ConnectOption {
-	return func(o *ConnectOptions) error {
-		o.Will = will
-		return nil
-	}
-}
-
 func (c *BaseClient) write(b []byte) error {
 	l := len(b)
 	c.muWrite.Lock()
diff --git a/client_test.go b/client_test.go
index 56d6a0e..a3745fe 100644
--- a/client_test.go
+++ b/client_test.go
@@ -20,6 +20,7 @@ func TestConnect(t *testing.T) {
 			WithUserNamePassword("user", "pass"),
 			WithKeepAlive(0x0123),
 			WithCleanSession(true),
+			WithProtocolLevel(ProtocolLevel4),
 			WithWill(&Message{QoS: QoS1, Topic: "topic", Payload: []byte{0x01}}),
 		)
 	}()
diff --git a/connect.go b/connect.go
index c3888dc..ff86951 100644
--- a/connect.go
+++ b/connect.go
@@ -6,10 +6,13 @@ import (
 	"io"
 )
 
-type protocolLevel byte
+// ProtocolLevel represents MQTT protocol level.
+type ProtocolLevel byte
 
+// ProtocolLevel values.
 const (
-	protocol311 protocolLevel = 0x04
+	ProtocolLevel3 ProtocolLevel = 0x03 // MQTT 3.1
+	ProtocolLevel4 ProtocolLevel = 0x04 // MQTT 3.1.1 (default)
 )
 
 type connectFlag byte
@@ -27,7 +30,9 @@ const (
 
 // Connect to the broker.
 func (c *BaseClient) Connect(ctx context.Context, clientID string, opts ...ConnectOption) (sessionPresent bool, err error) {
-	o := &ConnectOptions{}
+	o := &ConnectOptions{
+		ProtocolLevel: ProtocolLevel4,
+	}
 	for _, opt := range opts {
 		if err := opt(o); err != nil {
 			return false, err
@@ -86,7 +91,7 @@ func (c *BaseClient) Connect(ctx context.Context, clientID string, opts ...Conne
 		packetConnect.b(),
 		[]byte{
 			0x00, 0x04, 0x4D, 0x51, 0x54, 0x54,
-			byte(protocol311),
+			byte(o.ProtocolLevel),
 			flag,
 		},
 		packUint16(o.KeepAlive),
@@ -113,3 +118,57 @@ func (c *BaseClient) Connect(ctx context.Context, clientID string, opts ...Conne
 		return connAck.SessionPresent, nil
 	}
 }
+
+// ConnectOptions represents options for Connect.
+type ConnectOptions struct {
+	UserName      string
+	Password      string
+	CleanSession  bool
+	KeepAlive     uint16
+	Will          *Message
+	ProtocolLevel ProtocolLevel
+}
+
+// ConnectOption sets option for Connect.
+type ConnectOption func(*ConnectOptions) error
+
+// WithUserNamePassword sets plain text auth information used in Connect.
+func WithUserNamePassword(userName, password string) ConnectOption {
+	return func(o *ConnectOptions) error {
+		o.UserName = userName
+		o.Password = password
+		return nil
+	}
+}
+
+// WithKeepAlive sets keep alive interval in seconds.
+func WithKeepAlive(interval uint16) ConnectOption {
+	return func(o *ConnectOptions) error {
+		o.KeepAlive = interval
+		return nil
+	}
+}
+
+// WithCleanSession sets clean session flag.
+func WithCleanSession(cleanSession bool) ConnectOption {
+	return func(o *ConnectOptions) error {
+		o.CleanSession = cleanSession
+		return nil
+	}
+}
+
+// WithWill sets will message.
+func WithWill(will *Message) ConnectOption {
+	return func(o *ConnectOptions) error {
+		o.Will = will
+		return nil
+	}
+}
+
+// WithProtocolLevel sets protocol level.
+func WithProtocolLevel(level ProtocolLevel) ConnectOption {
+	return func(o *ConnectOptions) error {
+		o.ProtocolLevel = level
+		return nil
+	}
+}
diff --git a/mqtt.go b/mqtt.go
index 80f2b09..3ee390a 100644
--- a/mqtt.go
+++ b/mqtt.go
@@ -31,18 +31,6 @@ type Subscription struct {
 	QoS   QoS
 }
 
-// ConnectOptions represents options for Connect.
-type ConnectOptions struct {
-	UserName     string
-	Password     string
-	CleanSession bool
-	KeepAlive    uint16
-	Will         *Message
-}
-
-// ConnectOption sets option for Connect.
-type ConnectOption func(*ConnectOptions) error
-
 // Client is the interface of MQTT client.
 type Client interface {
 	Connect(ctx context.Context, clientID string, opts ...ConnectOption) (sessionPresent bool, err error)
diff --git a/paho/paho.go b/paho/paho.go
index d204d52..8eafe14 100644
--- a/paho/paho.go
+++ b/paho/paho.go
@@ -159,6 +159,7 @@ func (c *pahoWrapper) Connect() paho.Token {
 			mqtt.WithUserNamePassword(c.pahoConfig.Username, c.pahoConfig.Password),
 			mqtt.WithCleanSession(c.pahoConfig.CleanSession),
 			mqtt.WithKeepAlive(uint16(c.pahoConfig.KeepAlive)),
+			mqtt.WithProtocolLevel(mqtt.ProtocolLevel(c.pahoConfig.ProtocolVersion)),
 		}
 		if c.pahoConfig.WillEnabled {
 			opts = append(opts, mqtt.WithWill(&mqtt.Message{