diff --git a/bob/bio/base/test/test_config_file.py b/bob/bio/base/test/test_config_file.py
index a5bbed7fd503a77a5827a2fe391afc0281ba3358..f6e7cc0f26438f12bf3c2d00651797b1f3dbd559 100644
--- a/bob/bio/base/test/test_config_file.py
+++ b/bob/bio/base/test/test_config_file.py
@@ -54,6 +54,8 @@ def check_parameters(args_file, args_cmdline):
     if (isinstance(attr_file, (bool, str, int, list))) or (attr_file is None):
       assert attr_cmdline == attr_file, '(%s) %r != %r' % \
           (attr, attr_cmdline, attr_file)
+    else:
+      assert False, '(%s) %r == %r?' % (attr, attr_cmdline, attr_file)
 
 
 def test_basic():