diff --git a/libs/ardour/ardour/automation_list.h b/libs/ardour/ardour/automation_list.h
index 46643dc6fa..359d98856c 100644
--- a/libs/ardour/ardour/automation_list.h
+++ b/libs/ardour/ardour/automation_list.h
@@ -85,7 +85,7 @@ public:
 	bool paste (const ControlList&, double, DoubleBeatsFramesConverter const&);
 
 	void set_automation_state (AutoState);
-	AutoState automation_state() const { return _state; }
+	AutoState automation_state() const;
 	PBD::Signal1<void, AutoState> automation_state_changed;
 
 	bool automation_playback() const {
diff --git a/libs/ardour/automation_list.cc b/libs/ardour/automation_list.cc
index d92e65288f..3ffc040b62 100644
--- a/libs/ardour/automation_list.cc
+++ b/libs/ardour/automation_list.cc
@@ -192,16 +192,28 @@ AutomationList::maybe_signal_changed ()
 	}
 }
 
+AutoState
+AutomationList::automation_state() const
+{
+	Glib::Threads::RWLock::ReaderLock lm (Evoral::ControlList::_lock);
+	return _state;
+}
+
 void
 AutomationList::set_automation_state (AutoState s)
 {
-	if (s == _state) {
-		return;
-	}
-	_state = s;
-	if (s == Write && _desc.toggled) {
-		snapshot_history (true);
+	{
+		Glib::Threads::RWLock::ReaderLock lm (Evoral::ControlList::_lock);
+
+		if (s == _state) {
+			return;
+		}
+		_state = s;
+		if (s == Write && _desc.toggled) {
+			snapshot_history (true);
+		}
 	}
+
 	automation_state_changed (s); /* EMIT SIGNAL */
 }
 
@@ -588,4 +600,3 @@ AutomationListProperty::clone () const
 		boost::shared_ptr<AutomationList> (new AutomationList (*this->_current.get()))
 		);
 }
-