diff --git a/src/server/seat_interface.cpp b/src/server/seat_interface.cpp
--- a/src/server/seat_interface.cpp
+++ b/src/server/seat_interface.cpp
@@ -1346,7 +1346,7 @@
 qint32 SeatInterface::touchDown(const QPointF &globalPosition)
 {
     Q_D();
-    const qint32 id = d->globalTouch.ids.isEmpty() ? 0 : d->globalTouch.ids.last() + 1;
+    const qint32 id = d->globalTouch.ids.isEmpty() ? 0 : d->globalTouch.ids.lastKey() + 1;
     const qint32 serial = display()->nextSerial();
     const auto pos = globalPosition - d->globalTouch.focus.offset;
     for (auto it = d->globalTouch.focus.touchs.constBegin(), end = d->globalTouch.focus.touchs.constEnd(); it != end; ++it) {