diff --git a/libopenage/pathfinding/cost_field.h b/libopenage/pathfinding/cost_field.h
index decff980df..3750ed0680 100644
--- a/libopenage/pathfinding/cost_field.h
+++ b/libopenage/pathfinding/cost_field.h
@@ -160,7 +160,7 @@ class CostField {
 	/**
 	 * Cost field values.
 	 */
-	std::unordered_map<size_t, cost_stamp_t> cost_stamps;
+	std::vector<std::optional<cost_stamp_t>> cost_stamps;
 };
 
 } // namespace path