diff --git a/Client/UfrmMain.pas b/Client/UfrmMain.pas
index ca68e21..d3d004e 100644
--- a/Client/UfrmMain.pas
+++ b/Client/UfrmMain.pas
@@ -793,6 +793,9 @@ var
   cursorNeedsUpdate: Boolean;
   newZ: ShortInt;
 begin
+  if CurrentTile = nil then
+    Exit;
+
   //We want single steps ...
   WheelDelta := WheelDelta div WHEEL_DELTA;