diff --git a/tests/test_1_flattener.py b/tests/test_1_flattener.py
index 3d3e8c0c..764a8d81 100644
--- a/tests/test_1_flattener.py
+++ b/tests/test_1_flattener.py
@@ -55,10 +55,10 @@ def test_dir_error(request):
 
 def launch_flattener(test_dir, test_ok=False):
     eolobj = objspace.RougailObjSpace(Config['dtdfilename'])
-    dirs = [test_dir]
+    dirs = test_dir
     subfolder = join(test_dir, 'subfolder')
     if isdir(subfolder):
-        dirs.append(subfolder)
+        dirs = [dirs, subfolder]
     eolobj.create_or_populate_from_xml(Config['variable_namespace'], dirs)
     subfolder = join(test_dir, 'extra_dirs', 'extra')
     if isdir(subfolder):