diff --git a/exp/geometry.py b/exp/geometry.py
--- a/exp/geometry.py
+++ b/exp/geometry.py
@@ -13,7 +13,8 @@ class Line:
 	@staticmethod
 	def fromNormal(a,b,c):
 		"""ax + by + c = 0"""
-		norm=-c/abs(c)*math.sqrt(a**2+b**2)
+		sign=-c/abs(c) if c!=0 else 1
+		norm=sign*math.sqrt(a**2+b**2)
 		(a_,b_,c_)=(a/norm,b/norm,c/norm)
 		alpha=math.acos(a_) if b_>=0 else 2*math.pi-math.acos(a_)
 		return Line(alpha,-c_)