diff --git a/src/gui/imgview.py b/src/gui/imgview.py
--- a/src/gui/imgview.py
+++ b/src/gui/imgview.py
@@ -63,7 +63,7 @@ class ImgView(ResizableCanvas):
 	def addCorner(self,x,y):
 		self._corners.add(x,y)
 		log.debug("click on %d,%d",x,y)
-		if self._corners.canonizeOrder():
+		if self._corners.is_canon():
 			# transform corners from show coordinates to real coordinates
 			self._boardGrid=Grid(self._corners)
 			corners=[self._transformPoint(c) for c in self._corners]