diff --git a/squirrelbattle/entities/player.py b/squirrelbattle/entities/player.py
index dd4d6f0..45e2bdf 100644
--- a/squirrelbattle/entities/player.py
+++ b/squirrelbattle/entities/player.py
@@ -133,10 +133,11 @@ class Player(FightingEntity):
         # For each tile that is reached by at least one Dijkstra, sort the
         # different paths by distance to the player. For the technical bits :
         # The reduce function is a fold starting on the first element of the
-        # iterable, and we associate the points to their distance, sort 
+        # iterable, and we associate the points to their distance, sort
         # along the distance, then only keep the points.
         self.paths = {}
-        for y, x in reduce(set.union, [set(p.keys()) for p in predecessors]):
+        for y, x in reduce(set.union,
+                           [set(p.keys()) for p in predecessors], set()):
             self.paths[(y, x)] = [p for d, p in sorted(
                 [(distances[i][(y, x)], predecessors[i][(y, x)])
                  for i in range(len(distances)) if (y, x) in predecessors[i]])]