diff --git a/libs/temporal/tempo.cc b/libs/temporal/tempo.cc
index 338821950a..8ebaa52c20 100644
--- a/libs/temporal/tempo.cc
+++ b/libs/temporal/tempo.cc
@@ -2868,9 +2868,13 @@ TempoMap::twist_tempi (TempoSection* ts, const Tempo& bpm, const framepos_t fram
 void
 TempoMap::MementoBinder::set_state (XMLNode const & node, int version) const
 {
+	/* fetch a writable copy of this thread's tempo map */
 	TempoMap::SharedPtr map (write_copy());
+	/* change the state of the copy */
 	map->set_state (node, version);
+	/* do the update step of RCU */
 	update (map);
+	/* now update this thread's view of the current tempo map */
 	fetch ();
 }