diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 7afcd96978..1aa11f13cb 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -9911,7 +9911,7 @@ _gdk_windowing_got_event (GdkDisplay *display,
           if (source_device != pointer_info->last_slave &&
               gdk_device_get_device_type (source_device) == GDK_DEVICE_TYPE_SLAVE)
             pointer_info->last_slave = source_device;
-          else
+          else if (pointer_info->last_slave)
             source_device = pointer_info->last_slave;
         }