diff --git a/imapserver/imapmemserver/mailbox.go b/imapserver/imapmemserver/mailbox.go
index 88c156bf..9c2ffe02 100644
--- a/imapserver/imapmemserver/mailbox.go
+++ b/imapserver/imapmemserver/mailbox.go
@@ -454,7 +454,7 @@ func (mbox *MailboxView) staticNumSet(numSet imap.NumSet) imap.NumSet {
 
 	switch numSet := numSet.(type) {
 	case imap.SeqSet:
-		max := uint32(len(mbox.l))
+		max := mbox.tracker.EncodeNumMessages()
 		for i := range numSet {
 			r := &numSet[i]
 			staticNumRange(&r.Start, &r.Stop, max)
diff --git a/imapserver/tracker.go b/imapserver/tracker.go
index b22958cd..c615bdcf 100644
--- a/imapserver/tracker.go
+++ b/imapserver/tracker.go
@@ -282,3 +282,20 @@ func (t *SessionTracker) EncodeSeqNum(seqNum uint32) uint32 {
 	}
 	return seqNum
 }
+
+// EncodeNumMessages returns the number of messages in the mailbox from the
+// client point-of-view.
+func (t *SessionTracker) EncodeNumMessages() uint32 {
+	n := t.mailbox.numMessages
+	for i := len(t.queue) - 1; i >= 0; i-- {
+		update := t.queue[i]
+		// TODO: this doesn't handle increments > 1
+		if update.numMessages != 0 {
+			n--
+		}
+		if update.expunge != 0 {
+			n++
+		}
+	}
+	return n
+}