diff --git a/js/MaskTool.js b/js/MaskTool.js
index fc98c2f..309c382 100644
--- a/js/MaskTool.js
+++ b/js/MaskTool.js
@@ -23,8 +23,8 @@ export class MaskTool {
     }
 
     initMaskCanvas() {
-        this.maskCanvas.width = this.mainCanvas.width;
-        this.maskCanvas.height = this.mainCanvas.height;
+        this.maskCanvas.width = this.canvasInstance.width;
+        this.maskCanvas.height = this.canvasInstance.height;
         this.maskCtx.clearRect(0, 0, this.maskCanvas.width, this.maskCanvas.height);
     }