diff --git a/libs/ardour/port_manager.cc b/libs/ardour/port_manager.cc
index f801017478..688751df21 100644
--- a/libs/ardour/port_manager.cc
+++ b/libs/ardour/port_manager.cc
@@ -1487,6 +1487,11 @@ PortManager::run_input_meters (pframes_t n_samples, samplecnt_t rate)
 			continue;
 		}
 
+		if (_audio_port_meters.find (*p) == _audio_port_meters.end () || _audio_port_scopes.find (*p) == _audio_port_scopes.end ()) {
+			/* do not allocate ports during normal operation */
+			continue;
+		}
+
 		if (reset) {
 			_audio_port_meters[*p].reset ();
 		}
@@ -1530,6 +1535,11 @@ PortManager::run_input_meters (pframes_t n_samples, samplecnt_t rate)
 			continue;
 		}
 
+		if (_midi_port_meters.find (*p) == _midi_port_meters.end () || _midi_port_monitors.find (*p) == _midi_port_monitors.end ()) {
+			/* do not allocate ports during normal operation */
+			continue;
+		}
+
 		for (size_t i = 0; i < 17; ++i) {
 			/* falloff */
 			if (_midi_port_meters[*p].chn_active[i] > 1e-10) {