diff --git a/app.go b/app.go
index bd5d564..2c5947f 100644
--- a/app.go
+++ b/app.go
@@ -9455,6 +9455,15 @@ func (a *App) LogUDPLoggedADIF(adifText string) (int64, error) {
 	if a.qso == nil {
 		return 0, fmt.Errorf("db not initialized")
 	}
+	// Serialise the WHOLE operation — parse, callsign LOOKUP, dedup and insert —
+	// so simultaneous UDP QSOs are processed one at a time (a queue). A multi-stream
+	// MSHV finishing 4 QSOs at once used to fire 4 concurrent callsign lookups and DB
+	// writes, which the QRZ/HamQTH service (and a remote DB) rejected with "too many
+	// requests". Holding the lock across the lookup spaces them out; the UDP reader
+	// runs on its own goroutine, so this never blocks packet reception — callers just
+	// queue behind each other. (adifwatch shares this lock for the same reason.)
+	a.udpLogMu.Lock()
+	defer a.udpLogMu.Unlock()
 	// Pull the first record out of the payload. WSJT-X / JTDX / MSHV
 	// always send a single QSO per UDP packet (no header) but we tolerate
 	// either form via adif.Parse.
@@ -9597,12 +9606,10 @@ func (a *App) LogUDPLoggedADIF(adifText string) (int64, error) {
 	// a minute (the two apps stamp their own time), so a minute-exact key
 	// missed it and the contact got duplicated.
 	//
-	// The check + insert is guarded by udpLogMu: MSHV/WSJT can deliver the same
-	// logged-QSO packet twice in quick succession (re-broadcast, or two
-	// listeners), and without serialisation both goroutines read the dedup set
-	// BEFORE either inserts, both pass, and the QSO lands twice.
-	a.udpLogMu.Lock()
-	defer a.udpLogMu.Unlock()
+	// The check + insert is covered by udpLogMu (taken at the top of this function):
+	// MSHV/WSJT can deliver the same logged-QSO packet twice in quick succession
+	// (re-broadcast, or two listeners), and without serialisation both goroutines
+	// read the dedup set BEFORE either inserts, both pass, and the QSO lands twice.
 	seen, err := a.qso.ExistingDedupeKeys(a.ctx)
 	if err == nil {
 		base := q.QSODate.UTC()