diff --git a/libs/ardour/midi_source.cc b/libs/ardour/midi_source.cc
index d14a23d666..d12f23aff0 100644
--- a/libs/ardour/midi_source.cc
+++ b/libs/ardour/midi_source.cc
@@ -80,6 +80,8 @@ MidiSource::MidiSource (Session& s, const XMLNode& node)
 
 MidiSource::~MidiSource ()
 {
+	/* invalidate any existing iterators */
+	Invalidated (false);
 }
 
 XMLNode&