diff --git a/io_mesh_stl/stl_utils.py b/io_mesh_stl/stl_utils.py
index ff647b67efc0c74f66ac1f0b52a7308181071528..912df356a0c2f80a427ef48b1d66746ffd718fba 100644
--- a/io_mesh_stl/stl_utils.py
+++ b/io_mesh_stl/stl_utils.py
@@ -209,7 +209,7 @@ def read_stl(filename):
             # If the point is allready in the list of points, the
             # index returned by pts.add() will be the one from the
             # first equal point inserted.
-            tris.append(pts.add(p) for p in pt)
+            tris.append([pts.add(p) for p in pt])
 
     return tris, pts.list