diff --git a/source/Trek-12/Tests/RulesTests.cs b/source/Trek-12/Tests/RulesTests.cs
index 56ec387..9e495b8 100644
--- a/source/Trek-12/Tests/RulesTests.cs
+++ b/source/Trek-12/Tests/RulesTests.cs
@@ -35,7 +35,7 @@ public class RulesTests
         Map map = new Map("background");
         Cell selectedCell = map.Boards[0];
         selectedCell.Value = 5;
-        Assert.False(rules.IsCellValid(selectedCell, map.Boards));
+        Assert.False(rules.IsCellValid(selectedCell, map.Boards.ToList()));
     }
     
     [Fact]
@@ -44,7 +44,7 @@ public class RulesTests
         Rules rules = new Rules();
         Map map = new Map("background");
         Cell selectedCell = map.Boards[0];
-        Assert.True(rules.IsCellValid(selectedCell, map.Boards));
+        Assert.True(rules.IsCellValid(selectedCell, map.Boards.ToList()));
     }
     
     [Fact]
@@ -211,7 +211,7 @@ public class RulesTests
         Cell adjacentCell = new Cell(0, 1);
         adjacentCell.Value = 1;
         
-        map.Boards.Add(adjacentCell);
+        map.Boards.ToList().Add(adjacentCell);
         map.Zones.Add(new List<Cell> { adjacentCell });
         
         rules.IsZoneValidAndAddToZones(cell, map);
@@ -228,7 +228,7 @@ public class RulesTests
         Cell adjacentCell = new Cell(0, 1);
         adjacentCell.Value = 1;
         
-        map.Boards.Add(adjacentCell);
+        map.Boards.ToList().Add(adjacentCell);
         rules.IsZoneValidAndAddToZones(cell, map);
         Assert.Contains(cell, map.Zones[0]);
     }