diff --git a/basictypes.py b/basictypes.py
index 0e049e4..281401d 100644
--- a/basictypes.py
+++ b/basictypes.py
@@ -64,7 +64,10 @@ class StraightLine:
             raise WallIDMismatch('Wall ID for points does not match')
 
     def __find_line(self, p1:PointWithID, p2:PointWithID) -> tuple:
-        m = (p2.get_y() - p1.get_y()) / (p2.get_x() - p1.get_x())
+        try:
+            m = (p2.get_y() - p1.get_y()) / (p2.get_x() - p1.get_x())
+        except ZeroDivisionError:
+            m = None
         # Using p1 to find b
         b = p1.get_y() - (m*p1.get_x())
         # y = mx + b
@@ -75,6 +78,9 @@ class StraightLine:
         if p1.get_wallid() == p2.get_wallid(): return True
         return False
     
+    """
+    Return slope for non-virtical line. None for virtical lines
+    """
     def get_m(self)-> float:
         return self.m