diff --git a/htlcswitch/circuit_map.go b/htlcswitch/circuit_map.go
index a62067727..9b26a1d07 100644
--- a/htlcswitch/circuit_map.go
+++ b/htlcswitch/circuit_map.go
@@ -935,7 +935,7 @@ type Keystone struct {
 }
 
 // String returns a human readable description of the Keystone.
-func (k *Keystone) String() string {
+func (k Keystone) String() string {
 	return fmt.Sprintf("%s --> %s", k.InKey, k.OutKey)
 }
 
diff --git a/htlcswitch/mailbox.go b/htlcswitch/mailbox.go
index de85f7818..cc3bd1c83 100644
--- a/htlcswitch/mailbox.go
+++ b/htlcswitch/mailbox.go
@@ -548,6 +548,8 @@ func (m *memoryMailBox) mailCourier(cType courierType) {
 				m.pktCond.L.Unlock()
 
 			case <-deadline:
+				log.Debugf("Expiring add htlc with "+
+					"keystone=%v", add.keystone())
 				m.FailAdd(add)
 
 			case pktDone := <-m.pktReset:
diff --git a/htlcswitch/mailbox_test.go b/htlcswitch/mailbox_test.go
index b4fc8a6ec..9acb84d5f 100644
--- a/htlcswitch/mailbox_test.go
+++ b/htlcswitch/mailbox_test.go
@@ -294,7 +294,7 @@ func (c *mailboxContext) checkFails(adds []*htlcPacket) {
 
 	select {
 	case pkt := <-c.forwards:
-		c.t.Fatalf("unexpected forward: %v", pkt)
+		c.t.Fatalf("unexpected forward: %v", pkt.keystone())
 	case <-time.After(50 * time.Millisecond):
 	}
 }