diff --git a/ladybug_geometry/geometry2d/polygon.py b/ladybug_geometry/geometry2d/polygon.py
index 31ab515b..fe9af131 100644
--- a/ladybug_geometry/geometry2d/polygon.py
+++ b/ladybug_geometry/geometry2d/polygon.py
@@ -608,16 +608,18 @@ def remove_colinear_vertices(self, tolerance):
         """
         if len(self.vertices) == 3:
             return self  # Polygon2D cannot have fewer than 3 vertices
-        new_vertices = []
-        skip = 0
+        new_vertices = []  # list to hold the new vertices
+        skip = 0  # track the number of vertices being skipped/removed
+        # loop through vertices and remove all cases of colinear verts
         for i, _v in enumerate(self.vertices):
-            _a = self[i - 2].determinant(self[i - 1]) + self[i - 1].determinant(_v) + \
-                _v.determinant(self[i - 2])
+            _a = self[i - 2 - skip].determinant(self[i - 1]) + self[i - 1].determinant(_v) + \
+                _v.determinant(self[i - 2 - skip])
             if abs(_a) >= tolerance:
                 new_vertices.append(self[i - 1])
                 skip = 0
             else:
                 skip += 1
+        # catch case of last two vertices being equal but distinct from first point
         if skip != 0 and self.vertices[-2].is_equivalent(self.vertices[-1], tolerance):
             pts_2d = self.vertices
             _a = pts_2d[-3].determinant(pts_2d[-1]) + \
diff --git a/tests/face3d_test.py b/tests/face3d_test.py
index d36d69c9..f6b7b95a 100644
--- a/tests/face3d_test.py
+++ b/tests/face3d_test.py
@@ -1623,6 +1623,17 @@ def test_join_coplanar_faces():
     assert len(joined_faces[0].holes) == 5
 
 
+def test_join_coplanar_faces_advanced():
+    """Test the join_coplanar_faces method."""
+    geo_file = './tests/json/union_faces.json'
+    with open(geo_file, 'r') as fp:
+        geo_dict = json.load(fp)
+    join_faces = [Face3D.from_dict(fd) for fd in geo_dict]
+
+    join_face = Face3D.join_coplanar_faces(join_faces, 0.001)
+    assert sum(f.area for f in join_faces) == pytest.approx(join_face[0].area, rel=1e-3)
+
+
 def test_extract_all_from_stl():
     file_path = 'tests/stl/cube_binary.stl'
     faces = Face3D.extract_all_from_stl(file_path)
diff --git a/tests/json/union_faces.json b/tests/json/union_faces.json
new file mode 100644
index 00000000..50a33dc9
--- /dev/null
+++ b/tests/json/union_faces.json
@@ -0,0 +1 @@
+[{"type": "Face3D", "boundary": [[6.96093151743763, 1.2384060214181818, 2.9999999999999987], [8.290021124356151, 1.2384060214181818, 2.9999999999999987], [8.290021124356151, -0.7441439785816331, 2.9999999999999987], [6.960931517437629, -0.7441439785816288, 2.9999999999999987], [6.96093151743763, 1.2384060214181818, 2.9999999999999987]], "plane": {"type": "Plane", "n": [0.0, 0.0, -1.0], "o": [6.96093151743763, 1.2384060214181818, 2.9999999999999987], "x": [1.0, 0.0, 0.0]}}, {"type": "Face3D", "boundary": [[7.642481517437625, -0.7441439785816324, 2.9999999999999987], [10.001931517437628, -0.7441439785816344, 2.9999999999999987], [10.001931517437628, -3.302593978581496, 2.9999999999999987], [7.642481517437624, -3.302593978581496, 2.9999999999999987]], "plane": {"type": "Plane", "n": [0.0, 0.0, -1.0], "o": [7.642481517437625, -0.7441439785816324, 2.9999999999999987], "x": [1.0, 0.0, 0.0]}}, {"type": "Face3D", "boundary": [[6.859931517437632, 1.2384060214181867, 2.9999999999999987], [6.96093151743763, 1.2384060214181818, 2.9999999999999987], [6.960931517437629, -0.7441439785816288, 2.9999999999999987], [7.642481517437625, -0.7441439785816324, 2.9999999999999987], [7.642481517437624, -3.302593978581496, 2.9999999999999987], [7.001931517437624, -3.302593978581496, 2.9999999999999987], [7.001931517437626, -1.1455939785817102, 2.9999999999999987], [6.616831517437697, -1.1455939785817089, 2.9999999999999987], [6.6168315174376975, 1.3584060214181886, 2.9999999999999987], [6.859931517437632, 1.3584060214181877, 2.9999999999999987]], "plane": {"type": "Plane", "n": [0.0, 0.0, -1.0], "o": [6.859931517437632, 1.2384060214181867, 2.9999999999999987], "x": [1.0, 0.0, 0.0]}}, {"type": "Face3D", "boundary": [[10.001931517437628, 1.238406021418177, 2.9999999999999987], [10.001931517437628, -0.7441439785816344, 2.9999999999999987], [8.290021124356151, -0.7441439785816331, 2.9999999999999987], [8.290021124356151, 1.2384060214181818, 2.9999999999999987], [10.001931517437628, 1.238406021418177, 2.9999999999999987]], "plane": {"type": "Plane", "n": [0.0, 0.0, -1.0], "o": [10.001931517437628, 1.238406021418177, 2.9999999999999987], "x": [1.0, 0.0, 0.0]}}, {"type": "Face3D", "boundary": [[6.96093151743763, 1.2384060214181818, 2.9999999999999987], [6.859931517437632, 1.2384060214181867, 2.9999999999999987], [6.859931517437632, 1.3584060214181877, 2.9999999999999987], [10.001931517437628, 1.3584060214181772, 2.9999999999999987], [10.001931517437628, 1.238406021418177, 2.9999999999999987], [6.96093151743763, 1.2384060214181818, 2.9999999999999987]], "plane": {"type": "Plane", "n": [0.0, 0.0, -1.0], "o": [6.96093151743763, 1.2384060214181818, 2.9999999999999987], "x": [1.0, 0.0, 0.0]}}]
\ No newline at end of file