diff --git a/pycam/Geometry/Line.py b/pycam/Geometry/Line.py
index c0f1572e..92222bdd 100644
--- a/pycam/Geometry/Line.py
+++ b/pycam/Geometry/Line.py
@@ -189,9 +189,9 @@ def get_intersection(self, line, infinite_lines=False):
                 return None, None
             # the lines are on one straight
             candidates = []
-            if self.is_point_inside(x3):
+            if self.is_point_inside(x3) and pnorm(a) != 0:
                 candidates.append((x3, pnorm(c) / pnorm(a)))
-            elif self.is_point_inside(x4):
+            elif self.is_point_inside(x4) and pnorm(a) != 0:
                 candidates.append((x4, pdist(line.p2, self.p1) / pnorm(a)))
             elif line.is_point_inside(x1):
                 candidates.append((x1, 0))
diff --git a/pycam/Geometry/PointUtils.py b/pycam/Geometry/PointUtils.py
index 234afd23..7b59d8fd 100644
--- a/pycam/Geometry/PointUtils.py
+++ b/pycam/Geometry/PointUtils.py
@@ -76,6 +76,8 @@ def ptransform_by_matrix(a, matrix):
 
 def pmul(a, c):
     c = number(c)
+    if not a:
+        return (False, False, False)
     return (a[0] * c, a[1] * c, a[2] * c)
 
 
@@ -85,6 +87,13 @@ def pdiv(a, c):
 
 
 def padd(a, b):
+    if not (a and b):
+        if a:
+            return (a[0], a[1], a[2])
+        elif b:
+            return (b[0], b[1], b[2])
+        else:
+            return (None, None, None)
     return (a[0] + b[0], a[1] + b[1], a[2] + b[2])
 
 
diff --git a/pycam/Geometry/Polygon.py b/pycam/Geometry/Polygon.py
index c2457970..c5111cbb 100644
--- a/pycam/Geometry/Polygon.py
+++ b/pycam/Geometry/Polygon.py
@@ -231,8 +231,8 @@ def copy(self):
     def append(self, line):
         if not self.is_connectable(line):
             raise ValueError("This line does not fit to the polygon")
-        elif line.len < epsilon:
-            raise ValueError("A line with zero length may not be part of a polygon")
+        # elif line.len < epsilon:
+        #     raise ValueError("A line with zero length may not be part of a polygon")
         else:
             if not self._points:
                 self._points.append(line.p1)