diff -r db6ca177c6c4 -r 0d9ca37901ed geometry.py
--- a/geometry.py	Tue Jan 23 14:09:52 2018 +0200
+++ b/geometry.py	Tue Jan 23 15:30:48 2018 +0200
@@ -442,14 +442,22 @@
         a, b = line_1.vertices
         c, d = line_2.vertices
         try:
-            t = (intersection.x - a.x) / (b.x - a.x)
+            t1 = (intersection.x - a.x) / (b.x - a.x)
         except ZeroDivisionError:
-            t = inf
+            t1 = inf
+        try:
+            t2 = (intersection.x - c.x) / (d.x - c.x)
+        except ZeroDivisionError:
+            t2 = inf
         try:
-            u = (intersection.y - a.y) / (b.y - a.y)
+            u1 = (intersection.y - a.y) / (b.y - a.y)
         except ZeroDivisionError:
-            u = inf
-        if 0 < t < 1 or 0 < u < 1:
+            u1 = inf
+        try:
+            u2 = (intersection.y - c.y) / (d.y - c.y)
+        except ZeroDivisionError:
+            u2 = inf
+        if (0 < t1 < 1 and 0 < t2 < 1) or (0 < u1 < 1 and 0 < u2 < 1):
             return intersection
         else:
             return None