diff --git a/src/editor/editor_controller.cpp b/src/editor/editor_controller.cpp
index 6818446bdf4..54e57919c70 100644
--- a/src/editor/editor_controller.cpp
+++ b/src/editor/editor_controller.cpp
@@ -917,7 +917,7 @@ void editor_controller::toggle_grid()
 void editor_controller::unit_description()
 {
 	map_location loc = gui_->mouseover_hex();
-	unit_map units = context_manager_->get_map_context().get_units();
+	const unit_map & units = context_manager_->get_map_context().get_units();
 	const unit_map::const_unit_iterator un = units.find(loc);
 	if(un != units.end()) {
 		help::show_unit_help(*gui_, un->type_id(), false);