diff --git a/src/ifcblenderexport/blenderbim/bim/helper.py b/src/ifcblenderexport/blenderbim/bim/helper.py
index 9e598198d4..185f631121 100644
--- a/src/ifcblenderexport/blenderbim/bim/helper.py
+++ b/src/ifcblenderexport/blenderbim/bim/helper.py
@@ -329,49 +329,39 @@ def clip_segment(bounds, segm):
     """
     # Liang–Barsky algorithm
 
-    def iszero(v):
-        return abs(v) < 1e-10
-
     xmin, xmax, ymin, ymax = bounds
     p1, p2 = segm
 
+    def clip_side(p, q):
+        if abs(p) < 1e-10:  # ~= 0, parallel to the side
+            if q < 0:
+                return None  # outside
+            else:
+                return 0, 1  # inside
+
+        t = q / p  # the intersection point
+
+        if p < 0:  # entering
+            return t, 1
+        else:  # leaving
+            return 0, t
+
     dlt = p2 - p1
-    q_l = p1.x - xmin
-    q_r = xmax - p1.x
-    q_t = p1.y - ymin
-    q_b = ymax - p1.y
 
-    pos = [1]
-    neg = [0]
+    tt = (
+        clip_side(-dlt.x, p1.x - xmin),  # left
+        clip_side(+dlt.x, xmax - p1.x),  # right
+        clip_side(-dlt.y, p1.y - ymin),  # bottom
+        clip_side(+dlt.y, ymax - p1.y),  # top
+    )
 
-    if (iszero(dlt.x) and (q_l < 0 or q_r < 0)) or (iszero(dlt.y) and (q_t < 0 or q_b < 0)):
-        # parallel to a boundary and outside it
+    if None in tt:
         return None
 
-    if not iszero(dlt.x):
-        t_l = q_l / -dlt.x
-        t_r = q_r / dlt.x
-        if t_l < 0:
-            neg.append(t_l)
-            pos.append(t_r)
-        else:
-            neg.append(t_r)
-            pos.append(t_l)
+    t1 = max(0, max(t[0] for t in tt))
+    t2 = min(1, min(t[1] for t in tt))
 
-    if not iszero(dlt.y):
-        t_t = q_t / -dlt.y
-        t_b = q_b / dlt.y
-        if t_t < 0:
-            neg.append(t_t)
-            pos.append(t_b)
-        else:
-            neg.append(t_b)
-            pos.append(t_t)
-
-    t1 = max(neg)
-    t2 = min(pos)
-
-    if t1 > t2:
+    if t1 >= t2:
         return None
 
     p1c = p1 + dlt * t1
diff --git a/src/ifcblenderexport/runpytest.py b/src/ifcblenderexport/runpytest.py
new file mode 100755
index 0000000000..ec07e21d49
--- /dev/null
+++ b/src/ifcblenderexport/runpytest.py
@@ -0,0 +1,16 @@
+"""
+Requires pytest installed under blender
+
+Usage: `blender -b -P runpytest.py -- ARGS`
+"""
+
+import sys
+import pytest
+
+argv = [__file__]
+
+if '--' in sys.argv:
+    i = sys.argv.index('--')
+    argv += sys.argv[i+1:]
+
+pytest.main(argv)
diff --git a/src/ifcblenderexport/tests/test_segment_clipping.py b/src/ifcblenderexport/tests/test_segment_clipping.py
new file mode 100644
index 0000000000..d36291fbe1
--- /dev/null
+++ b/src/ifcblenderexport/tests/test_segment_clipping.py
@@ -0,0 +1,53 @@
+import pytest
+from mathutils import Vector
+
+from blenderbim.bim.helper import clip_segment
+
+
+BOUNDS = (10, 30, 10, 30)
+
+SEGMENTS_INSIDE = (
+    (Vector((15, 20)), Vector((25, 20))),
+    (Vector((20, 15)), Vector((20, 25))),
+    (Vector((15, 15)), Vector((25, 25))),
+    (Vector((15, 25)), Vector((25, 15))),
+)
+
+SEGMENTS_OUTSIDE = (
+    (Vector((15, 35)), Vector((25, 35))),
+    (Vector((25, 35)), Vector((35, 25))),
+    (Vector((35, 25)), Vector((35, 15))),
+    (Vector((35, 15)), Vector((25, 5))),
+    (Vector((25, 5)), Vector((15, 5))),
+    (Vector((15, 5)), Vector((5, 15))),
+    (Vector((5, 15)), Vector((5, 25))),
+    (Vector((5, 25)), Vector((15, 35)))
+)
+
+SEGMENTS_CLIPPED = (
+    ((Vector((5, 20)), Vector((15, 20))), (Vector((10, 20)), Vector((15, 20)))),
+    ((Vector((25, 20)), Vector((35, 20))), (Vector((25, 20)), Vector((30, 20)))),
+    ((Vector((20, 5)), Vector((20, 15))), (Vector((20, 10)), Vector((20, 15)))),
+    ((Vector((20, 15)), Vector((20, 35))), (Vector((20, 15)), Vector((20, 30)))),
+    ((Vector((5, 20)), Vector((20, 35))), (Vector((10, 25)), Vector((15, 30)))),
+    ((Vector((5, 20)), Vector((20, 5))), (Vector((10, 15)), Vector((15, 10)))),
+    ((Vector((35, 20)), Vector((20, 35))), (Vector((30, 25)), Vector((25, 30)))),
+    ((Vector((35, 20)), Vector((20, 5))), (Vector((30, 15)), Vector((25, 10)))),
+)
+
+@pytest.mark.parametrize('segment', SEGMENTS_INSIDE)
+def test_clip_inside(segment):
+    clipped = clip_segment(BOUNDS, segment)
+    assert clipped == segment
+
+
+@pytest.mark.parametrize('segment', SEGMENTS_OUTSIDE)
+def test_clip_outside(segment):
+    clipped = clip_segment(BOUNDS, segment)
+    assert clipped is None
+
+
+@pytest.mark.parametrize('segment,expected', SEGMENTS_CLIPPED)
+def test_clip_crossing(segment, expected):
+    clipped = clip_segment(BOUNDS, segment)
+    assert clipped == expected