diff --git a/thinkcspy/Chapter-17-18-Exercises/points.py b/thinkcspy/Chapter-17-18-Exercises/points.py
index 23ac392..10c5aa2 100644
--- a/thinkcspy/Chapter-17-18-Exercises/points.py
+++ b/thinkcspy/Chapter-17-18-Exercises/points.py
@@ -31,6 +31,9 @@ class Point:
         return (self.x, -self.y)
     
     def slopeFromOrigin(self):
+        if self.x == 0:
+            return None
+        
         return self.y / self.x
     
     def slopeIntercept(self, pnt):
@@ -79,3 +82,5 @@ class Point:
     def __str__(self):
         return "x=" + str(self.x) + ", y=" + str(self.y)
     
+p = Point(0, 5)
+print(p.slopeFromOrigin())