diff --git a/Liner/Liner/AbstractMap.cs b/Liner/Liner/AbstractMap.cs
index 24284e4..21ceac2 100644
--- a/Liner/Liner/AbstractMap.cs
+++ b/Liner/Liner/AbstractMap.cs
@@ -146,7 +146,7 @@ namespace Liner
             {
                 return false;
             }
-            var otherMap = other;
+            var otherMap = other as AbstractMap;
             if(otherMap == null) 
             {
                 return false;