diff --git a/io_mesh_stl/blender_utils.py b/io_mesh_stl/blender_utils.py
index a043a8f34c65eba4090c1f90995ac64e17a89b16..751f258634636252eb1dced8cb7c67a435ceaa49 100644
--- a/io_mesh_stl/blender_utils.py
+++ b/io_mesh_stl/blender_utils.py
@@ -38,16 +38,20 @@ def faces_from_mesh(ob, apply_modifier=False, triangulate=True):
     except SystemError:
         return ()
 
-    def iter_face_index():
-        '''
-        From a list of faces, return the face triangulated if needed.
-        '''
-        for face in mesh.faces:
-            if triangulate and len(face.vertices) == 4:
-                yield face.vertices[:3]
-                yield face.vertices[2:] + [face.vertices[0]]
-            else:
-                yield list(face.vertices)
-
-    return ([tuple(mesh.vertices[index].co * ob.matrix_world)
+    if triangulate:
+        # From a list of faces, return the face triangulated if needed.
+        def iter_face_index():
+            for face in mesh.faces:
+                vertices = face.vertices[:]
+                if len(vertices) == 4:
+                    yield vertices[0], vertices[1], vertices[2]
+                    yield vertices[2], vertices[3], vertices[0]
+                else:
+                    yield vertices
+    else:
+        def iter_face_index():
+            for face in mesh.faces:
+                yield face.vertices[:]
+
+    return ([(mesh.vertices[index].co * ob.matrix_world)[:]
              for index in indexes] for indexes in iter_face_index())
diff --git a/io_mesh_stl/stl_utils.py b/io_mesh_stl/stl_utils.py
index 734204b8dd16c2a4b8c447897ab29f353da92f17..9524ecb3dcfafcd9df87d093591d30ade02233e8 100644
--- a/io_mesh_stl/stl_utils.py
+++ b/io_mesh_stl/stl_utils.py
@@ -65,6 +65,7 @@ class ListDict(dict):
 BINARY_HEADER = 80
 BINARY_STRIDE = 12 * 4 + 2
 
+
 def _is_ascii_file(data):
     '''
     This function returns True if the data represents an ASCII file.
@@ -77,6 +78,7 @@ def _is_ascii_file(data):
 
     return not data.size() == BINARY_HEADER + 4 + BINARY_STRIDE * size
 
+
 def _binary_read(data):
     # an stl binary file is
     # - 80 bytes of description