diff --git a/src/main/java/ch/fritteli/labyrinth/model/Walls.java b/src/main/java/ch/fritteli/labyrinth/model/Walls.java
index 78f82f4..332be6e 100644
--- a/src/main/java/ch/fritteli/labyrinth/model/Walls.java
+++ b/src/main/java/ch/fritteli/labyrinth/model/Walls.java
@@ -6,9 +6,11 @@ import lombok.NonNull;
 import java.util.EnumSet;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.SortedSet;
+import java.util.TreeSet;
 
 public class Walls {
-    private final Set<Direction> directions = new HashSet<>();
+    private final SortedSet<Direction> directions = new TreeSet<>();
     private final Set<Direction> hardened = new HashSet<>();
 
     public boolean set(@NonNull final Direction direction) {