diff --git a/pyzkb/pyzkb.py b/pyzkb/pyzkb.py
index c0989d7..79e3863 100755
--- a/pyzkb/pyzkb.py
+++ b/pyzkb/pyzkb.py
@@ -80,6 +80,8 @@ class ZKillboard(object):
                     raise InvalidModifier('%s is a unknown modifier' % mod_name)
                 if args is None and mod_name.lower() in ZKillboard._MODIFIERS_ARGUMENT:
                     raise InvalidModifier('%s requires a argument' % mod_name)
+                if args and mod_name.lower() not in ZKillboard._MODIFIERS_ARGUMENT:
+                    raise InvalidModifier('%s does not require an argument' % mod_name)
                 if args and isinstance(args, list) and len(args) > 10:
                     raise ValueError('No more than 10 IDs are allowed at a time')
             x = copy.deepcopy(self)
diff --git a/tests/test_pyzkb.py b/tests/test_pyzkb.py
index f69c7e1..a8aae7b 100755
--- a/tests/test_pyzkb.py
+++ b/tests/test_pyzkb.py
@@ -57,9 +57,9 @@ class TestZKillboard(unittest.TestCase):
         self.assertTrue(len(x._modifiers) == 1)
 
     def test_xml_format_set(self):
-        self.kb.xml()
-        self.assertTrue(len(self.kb._modifiers), 1)
-        self.assertTrue(self.kb._xml_format)
+        x = self.kb.xml()
+        self.assertTrue(len(x._modifiers), 1)
+        self.assertTrue(x._xml_format)
 
     def tearDown(self):
         pass