diff --git a/gtk2_ardour/ardour_ui_options.cc b/gtk2_ardour/ardour_ui_options.cc
index 29c71a61a8..ecb5766c16 100644
--- a/gtk2_ardour/ardour_ui_options.cc
+++ b/gtk2_ardour/ardour_ui_options.cc
@@ -69,6 +69,8 @@ when the pull up/down setting is non-zero."));
 			}
 		}
 
+		ActionManager::toggle_config_state_foo ("Transport", "ToggleExternalSync", sigc::mem_fun (_session->config, &SessionConfiguration::set_external_sync), sigc::mem_fun (_session->config, &SessionConfiguration::get_external_sync));
+
 		/* activating a slave is a session-property.
 		 * The slave type is a RC property.
 		 * When the slave is active is must not be reconfigured.
@@ -79,8 +81,6 @@ when the pull up/down setting is non-zero."));
 		 * status changed:
 		 */
 		Config->ParameterChanged("sync-source");
-
-		ActionManager::toggle_config_state_foo ("Transport", "ToggleExternalSync", sigc::mem_fun (_session->config, &SessionConfiguration::set_external_sync), sigc::mem_fun (_session->config, &SessionConfiguration::get_external_sync));
 	}
 }
 
diff --git a/gtk2_ardour/rc_option_editor.cc b/gtk2_ardour/rc_option_editor.cc
index e8486ed5c0..91c3cda737 100644
--- a/gtk2_ardour/rc_option_editor.cc
+++ b/gtk2_ardour/rc_option_editor.cc
@@ -1812,7 +1812,7 @@ RCOptionEditor::parameter_changed (string const & p)
 	} else if (p == "sync-source") {
 		_sync_source->set_sensitive (true);
 		if (_session) {
-			_sync_source->set_sensitive (_session->config.get_external_sync());
+			_sync_source->set_sensitive (!_session->config.get_external_sync());
 		}
 		switch(Config->get_sync_source()) {
 		case ARDOUR::MTC: