diff --git a/libs/evoral/ControlList.cc b/libs/evoral/ControlList.cc
index c4380599ad..a4bf412c1f 100644
--- a/libs/evoral/ControlList.cc
+++ b/libs/evoral/ControlList.cc
@@ -264,7 +264,7 @@ ControlList::x_scale (ratio_t const & factor)
 }
 
 timepos_t
-ControlList::ensure_time_domain (timepos_t const & val)
+ControlList::ensure_time_domain (timepos_t const & val) const
 {
 	if (val.time_domain() != _time_domain) {
 		switch (_time_domain) {
diff --git a/libs/evoral/evoral/ControlList.h b/libs/evoral/evoral/ControlList.h
index 48bc799e38..99258e788a 100644
--- a/libs/evoral/evoral/ControlList.h
+++ b/libs/evoral/evoral/ControlList.h
@@ -412,7 +412,7 @@ public:
 	void add_guard_point (Temporal::timepos_t const & when, Temporal::timecnt_t const & offset);
 
 	bool is_sorted () const;
-	Temporal::timepos_t ensure_time_domain (Temporal::timepos_t const & );
+	Temporal::timepos_t ensure_time_domain (Temporal::timepos_t const & ) const;
 
 };