diff --git a/pelita/maze_generator.py b/pelita/maze_generator.py
index ccd796571..e51ed5b78 100644
--- a/pelita/maze_generator.py
+++ b/pelita/maze_generator.py
@@ -97,7 +97,7 @@ def sample_nodes(nodes, k, rng=None):
     if k < len(nodes):
         return set(rng.sample(sorted(nodes), k=k))
     else:
-        return nodes
+        return set(nodes)
 
 
 def distribute_food(all_tiles, chamber_tiles, trapped_food, total_food, rng=None):