diff --git a/exp/board_detect.py b/exp/board_detect.py
--- a/exp/board_detect.py
+++ b/exp/board_detect.py
@@ -246,6 +246,7 @@ class BoardDetector:
 		return sum(self._hough.scoreLine(p.transform(self._inverseMatrix)) for p in itertools.chain(*lines))
 
 	def detectPosition(self,img):
+		if not self.grid: return None
 		(rows,cols)=self.grid
 		intersections=[[row.intersect(col) for col in cols] for row in rows]
 		position=[[self._detectStoneAt(img,point) for point in row] for row in intersections]