diff --git a/libs/surfaces/generic_midi/midicontrollable.cc b/libs/surfaces/generic_midi/midicontrollable.cc
index f866bab2bb..f721e7fbbc 100644
--- a/libs/surfaces/generic_midi/midicontrollable.cc
+++ b/libs/surfaces/generic_midi/midicontrollable.cc
@@ -210,6 +210,7 @@ MIDIControllable::lookup_controllable()
 void
 MIDIControllable::drop_controllable ()
 {
+	cerr << "removed controllable\n";
 	controllable_death_connection.disconnect ();
 	controllable = 0;
 }
@@ -243,6 +244,8 @@ MIDIControllable::midi_sense_controller (Parser &, EventTwoBytes *msg)
 		}
 	}
 
+	assert (controllable);
+
 	if (controllable->touching()) {
 		return; // to prevent feedback fights when e.g. dragging a UI slider
 	}