diff --git a/plugins/UFPWriter/UFPWriter.py b/plugins/UFPWriter/UFPWriter.py
index a48a6a794e..06c3cce14e 100644
--- a/plugins/UFPWriter/UFPWriter.py
+++ b/plugins/UFPWriter/UFPWriter.py
@@ -29,4 +29,6 @@ class UFPWriter(MeshWriter):
         thumbnail = archive.getStream("/Metadata/thumbnail.png")
         thumbnail.write(open(os.path.join(os.path.dirname(__file__), "kitten.png"), "rb").read())
         thumbnail.close()
-        archive.addRelation(virtual_path = "/Metadata/thumbnail.png", file_type = "http://schemas.openxmlformats.org/package/2006/relationships/metadata/thumbnail")
\ No newline at end of file
+        archive.addRelation(virtual_path = "/Metadata/thumbnail.png", file_type = "http://schemas.openxmlformats.org/package/2006/relationships/metadata/thumbnail")
+
+        archive.close()
\ No newline at end of file