diff --git a/vorlesung/L08_graphen/graph.py b/vorlesung/L08_graphen/graph.py
index af94fd4..f3f5da5 100644
--- a/vorlesung/L08_graphen/graph.py
+++ b/vorlesung/L08_graphen/graph.py
@@ -127,7 +127,7 @@ class Graph:
             predecessor_map[vertex] = None
 
         while white_vertices:
-            v = white_vertices.pop()
+            v = next(iter(white_vertices))
             dfs_visit(v)
 
         return enter_map, leave_map, predecessor_map