diff --git a/whisper/whisperv6/api.go b/whisper/whisperv6/api.go
index 2de99f293..e0c3284b6 100644
--- a/whisper/whisperv6/api.go
+++ b/whisper/whisperv6/api.go
@@ -285,7 +285,7 @@ func (api *PublicWhisperAPI) Post(ctx context.Context, req NewMessage) (hexutil.
 	}
 
 	var result []byte
-	env, err := whisperMsg.Wrap(params)
+	env, err := whisperMsg.Wrap(params, api.w.GetCurrentTime())
 	if err != nil {
 		return nil, err
 	}
diff --git a/whisper/whisperv6/config.go b/whisper/whisperv6/config.go
index 61419de00..3c28263e5 100644
--- a/whisper/whisperv6/config.go
+++ b/whisper/whisperv6/config.go
@@ -16,14 +16,18 @@
 
 package whisperv6
 
+import "time"
+
 // Config represents the configuration state of a whisper node.
 type Config struct {
 	MaxMessageSize     uint32  `toml:",omitempty"`
 	MinimumAcceptedPOW float64 `toml:",omitempty"`
+	TimeSource         func() time.Time
 }
 
 // DefaultConfig represents (shocker!) the default configuration.
 var DefaultConfig = Config{
 	MaxMessageSize:     DefaultMaxMessageSize,
 	MinimumAcceptedPOW: DefaultMinimumPoW,
+	TimeSource:         time.Now,
 }
diff --git a/whisper/whisperv6/envelope.go b/whisper/whisperv6/envelope.go
index c42d1fa8a..3b65fdba0 100644
--- a/whisper/whisperv6/envelope.go
+++ b/whisper/whisperv6/envelope.go
@@ -62,9 +62,9 @@ func (e *Envelope) rlpWithoutNonce() []byte {
 
 // NewEnvelope wraps a Whisper message with expiration and destination data
 // included into an envelope for network forwarding.
-func NewEnvelope(ttl uint32, topic TopicType, msg *sentMessage) *Envelope {
+func NewEnvelope(ttl uint32, topic TopicType, msg *sentMessage, now time.Time) *Envelope {
 	env := Envelope{
-		Expiry: uint32(time.Now().Add(time.Second * time.Duration(ttl)).Unix()),
+		Expiry: uint32(now.Add(time.Second * time.Duration(ttl)).Unix()),
 		TTL:    ttl,
 		Topic:  topic,
 		Data:   msg.Raw,
diff --git a/whisper/whisperv6/message.go b/whisper/whisperv6/message.go
index 2d4e86244..a12b445e2 100644
--- a/whisper/whisperv6/message.go
+++ b/whisper/whisperv6/message.go
@@ -27,6 +27,7 @@ import (
 	"errors"
 	mrand "math/rand"
 	"strconv"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
@@ -234,7 +235,7 @@ func generateSecureRandomData(length int) ([]byte, error) {
 }
 
 // Wrap bundles the message into an Envelope to transmit over the network.
-func (msg *sentMessage) Wrap(options *MessageParams) (envelope *Envelope, err error) {
+func (msg *sentMessage) Wrap(options *MessageParams, now time.Time) (envelope *Envelope, err error) {
 	if options.TTL == 0 {
 		options.TTL = DefaultTTL
 	}
@@ -254,7 +255,7 @@ func (msg *sentMessage) Wrap(options *MessageParams) (envelope *Envelope, err er
 		return nil, err
 	}
 
-	envelope = NewEnvelope(options.TTL, options.Topic, msg)
+	envelope = NewEnvelope(options.TTL, options.Topic, msg, now)
 	if err = envelope.Seal(options); err != nil {
 		return nil, err
 	}
diff --git a/whisper/whisperv6/whisper.go b/whisper/whisperv6/whisper.go
index 8d56ece64..697f0ecb8 100644
--- a/whisper/whisperv6/whisper.go
+++ b/whisper/whisperv6/whisper.go
@@ -92,6 +92,8 @@ type Whisper struct {
 	envelopeTracer EnvelopeTracer // Service collecting envelopes metadata
 
 	envelopeFeed event.Feed
+
+	timeSource func() time.Time // source of time for whisper
 }
 
 // New creates a Whisper client ready to communicate through the Ethereum P2P network.
@@ -110,6 +112,7 @@ func New(cfg *Config) *Whisper {
 		p2pMsgQueue:   make(chan *Envelope, messageQueueLimit),
 		quit:          make(chan struct{}),
 		syncAllowance: DefaultSyncAllowance,
+		timeSource:    cfg.TimeSource,
 	}
 
 	whisper.filters = NewFilters(whisper)
@@ -215,6 +218,11 @@ func (whisper *Whisper) APIs() []rpc.API {
 	}
 }
 
+// GetCurrentTime returns current time.
+func (whisper *Whisper) GetCurrentTime() time.Time {
+	return whisper.timeSource()
+}
+
 // RegisterServer registers MailServer interface.
 // MailServer will process all the incoming messages with p2pRequestCode.
 func (whisper *Whisper) RegisterServer(server MailServer) {
@@ -829,7 +837,7 @@ func (whisper *Whisper) runMessageLoop(p *Peer, rw p2p.MsgReadWriter) error {
 // appropriate time-stamp. In case of error, connection should be dropped.
 // param isP2P indicates whether the message is peer-to-peer (should not be forwarded).
 func (whisper *Whisper) add(envelope *Envelope, isP2P bool) (bool, error) {
-	now := uint32(time.Now().Unix())
+	now := uint32(whisper.timeSource().Unix())
 	sent := envelope.Expiry - envelope.TTL
 
 	if sent > now {
@@ -988,7 +996,7 @@ func (whisper *Whisper) expire() {
 	whisper.statsMu.Lock()
 	defer whisper.statsMu.Unlock()
 	whisper.stats.reset()
-	now := uint32(time.Now().Unix())
+	now := uint32(whisper.timeSource().Unix())
 	for expiry, hashSet := range whisper.expirations {
 		if expiry < now {
 			// Dump all expired messages and remove timestamp