diff --git a/dotscape b/dotscape
index db63536..8765674 100755
Binary files a/dotscape and b/dotscape differ
diff --git a/fcore/app-with.sml b/fcore/app-with.sml
index f52d8f9..f749b20 100644
--- a/fcore/app-with.sml
+++ b/fcore/app-with.sml
@@ -1000,7 +1000,7 @@ struct
       }
     end
 
-  fun useLayerTree (app: app_type, layerTree, canvasWidth, canvasHeight) :
+  fun parsedLayerTree (app: app_type, layerTree, canvasWidth, canvasHeight) :
     app_type =
     let
       val
@@ -1028,6 +1028,11 @@ struct
         , layerTree = _
         , modalNum
         } = app
+
+      val arrowX =
+        if canvasWidth = 0 then 0 else Int.min (canvasWidth - 1, arrowX)
+      val arrowY =
+        if canvasHeight = 0 then 0 else Int.min (canvasHeight - 1, arrowY)
     in
       { mode = mode
       , mouseX = mouseX
diff --git a/fcore/normal-mode.sml b/fcore/normal-mode.sml
index a8f88bf..402fef5 100644
--- a/fcore/normal-mode.sml
+++ b/fcore/normal-mode.sml
@@ -337,7 +337,7 @@ struct
   fun useLayers (model, layerTree, canvasWidth, canvasHeight) =
     let
       val model =
-        AppWith.layerTree (model, layerTree, canvasWidth, canvasHeight)
+        AppWith.parsedLayerTree (model, layerTree, canvasWidth, canvasHeight)
     in
       getDrawMessage model
     end