diff --git a/src/c3nav/routing/router.py b/src/c3nav/routing/router.py
index f7515def..d9af611f 100644
--- a/src/c3nav/routing/router.py
+++ b/src/c3nav/routing/router.py
@@ -223,7 +223,7 @@ class Router:
         # respect slow_down_factor
         for area in areas.values():
             if area.slow_down_factor != 1:
-                area_nodes = np.array(area.nodes, dtype=np.uint32)
+                area_nodes = np.array(tuple(area.nodes), dtype=np.uint32)
                 graph[area_nodes.reshape((-1, 1)), area_nodes] *= float(area.slow_down_factor)
 
         # finalize waytype matrixes