diff --git a/TODO.taskpaper b/TODO.taskpaper
--- a/TODO.taskpaper
+++ b/TODO.taskpaper
@@ -233,6 +233,6 @@
 			May be due to a quirk of my Linux setup
 		- Drawing error when clicking sometimes on main screen. @done(2022-04-27)
 			Tries to draw area?
-		- Crash when extending preserve past bottom.
+		- Crash when extending preserve past bottom. @done(2022-04-27)
 			
 
diff --git a/isometric-park-fna/Engines/BuildToolEngine.cs b/isometric-park-fna/Engines/BuildToolEngine.cs
--- a/isometric-park-fna/Engines/BuildToolEngine.cs
+++ b/isometric-park-fna/Engines/BuildToolEngine.cs
@@ -136,8 +136,8 @@
 
                                 var newSquares = new List<Vector2>();
 
-                                var end_x = MathUtils.Clamp(message.End.X, 0.0f, this.Map.MapWidth);
-                                var end_y = MathUtils.Clamp(message.End.Y, 0.0f, this.Map.MapHeight);
+                                var end_x = MathUtils.Clamp(message.End.X, 0.0f, this.Map.MapWidth-1);
+                                var end_y = MathUtils.Clamp(message.End.Y, 0.0f, this.Map.MapHeight-1);
 
                                 foreach (var i in step_until(area.squares[0].X, end_x)) {
                                     foreach (var j in step_until(area.squares[0].Y, end_y)) {