diff --git a/mlat/client/coordinator.py b/mlat/client/coordinator.py
index 571fb34..8abce02 100644
--- a/mlat/client/coordinator.py
+++ b/mlat/client/coordinator.py
@@ -162,7 +162,7 @@ def update_aircraft(self, now):
         self.last_aircraft_update = now
 
     def send_aircraft_report(self):
-        all_aircraft = {x.icao for x in self.aircraft.values()}
+        all_aircraft = {x.icao for x in self.aircraft.values() if x.messages > 1}
         seen_ac = all_aircraft.difference(self.reported)
         lost_ac = self.reported.difference(all_aircraft)
 
@@ -195,6 +195,9 @@ def periodic_stats(self, now):
         adsb_req = adsb_total = modes_req = modes_total = 0
         now = monotonic_time()
         for ac in self.aircraft.values():
+            if ac.messages < 2:
+                continue
+
             if now - ac.last_position_time < self.position_expiry_age:
                 adsb_total += 1
                 if ac.requested:
diff --git a/modes_reader.c b/modes_reader.c
index 039a32e..c7f8b17 100644
--- a/modes_reader.c
+++ b/modes_reader.c
@@ -1261,9 +1261,14 @@ static int filter_message(modesreader *self, PyObject *o)
     }
 
     if (self->seen != NULL && self->seen != Py_None) {
-        /* note that we saw this aircraft, even if the message is filtered */
-        if (PySet_Add(self->seen, message->address) < 0) {
-            return -1;
+        if (message->df == 11 || message->df == 17 || message->df == 18) {
+            /* note that we saw this aircraft, even if the message is filtered.
+             * only do this for CRC-checked messages as we get a lot of noise
+             * otherwise.
+             */
+            if (PySet_Add(self->seen, message->address) < 0) {
+                return -1;
+            }
         }
     }