diff --git a/src/github.com/kentik/libkflow/main.go b/src/github.com/kentik/libkflow/main.go
index b44967d..65d844e 100644
--- a/src/github.com/kentik/libkflow/main.go
+++ b/src/github.com/kentik/libkflow/main.go
@@ -66,7 +66,7 @@ func kflowSend(cflow *C.kflow) C.int {
 
 	for i, c := range customs {
 		name := C.GoString(c.name)
-		id, ok := sender.Customs[name]
+		id, ok := sender.Device.Customs[name]
 		if !ok {
 			return C.EKFLOWNOCUSTOM
 		}
diff --git a/src/github.com/kentik/libkflow/send.go b/src/github.com/kentik/libkflow/send.go
index 96d8632..ae1f752 100644
--- a/src/github.com/kentik/libkflow/send.go
+++ b/src/github.com/kentik/libkflow/send.go
@@ -20,7 +20,7 @@ type Sender struct {
 	Timeout time.Duration
 	Client  *api.Client
 	Verbose int
-	Customs api.CustomColumns
+	Device  *api.Device
 	workers sync.WaitGroup
 }
 
@@ -42,7 +42,7 @@ func (s *Sender) Start(agg *agg.Agg, client *api.Client, device *api.Device, n i
 
 	s.Agg = agg
 	s.URL.RawQuery = q.Encode()
-	s.Customs = device.Customs
+	s.Device = device
 	s.Client = client
 	s.workers.Add(n)
 
@@ -62,6 +62,7 @@ func (s *Sender) Segment() *capnp.Segment {
 
 func (s *Sender) Send(flow *chf.CHF) {
 	s.debug("sending flow to aggregator")
+	flow.SetDeviceId(uint32(s.Device.ID))
 	s.Agg.Add(flow)
 }
 
diff --git a/src/github.com/kentik/libkflow/send_test.go b/src/github.com/kentik/libkflow/send_test.go
index ff91850..28bc49f 100644
--- a/src/github.com/kentik/libkflow/send_test.go
+++ b/src/github.com/kentik/libkflow/send_test.go
@@ -33,6 +33,24 @@ func TestSender(t *testing.T) {
 	assert.Equal(expected.String(), msgs.At(0).String())
 }
 
+func TestSenderFields(t *testing.T) {
+	sender, server, assert := setup(t)
+
+	expected, err := chf.NewCHF(sender.Segment())
+	if err != nil {
+		t.Fatal(err)
+	}
+	sender.Send(&expected)
+
+	msgs, err := (<-server.Flows()).Msgs()
+	if err != nil {
+		t.Fatal(err)
+	}
+	actual := msgs.At(0)
+
+	assert.EqualValues(sender.Device.ID, actual.DeviceId())
+}
+
 func TestSenderStop(t *testing.T) {
 	sender, _, assert := setup(t)
 	stopped := sender.Stop(100 * time.Millisecond)