diff --git a/pandas/core/config.py b/pandas/core/config.py
index 3e8d76500d128..60dc1d7d0341e 100644
--- a/pandas/core/config.py
+++ b/pandas/core/config.py
@@ -445,7 +445,7 @@ def register_option(key, defval, doc='', validator=None, cb=None):
     for k in path:
         if not bool(re.match('^' + tokenize.Name + '$', k)):
             raise ValueError("%s is not a valid identifier" % k)
-        if keyword.iskeyword(key):
+        if keyword.iskeyword(k):
             raise ValueError("%s is a python keyword" % k)
 
     cursor = _global_config
diff --git a/pandas/tests/test_config.py b/pandas/tests/test_config.py
index e60c9d5bd0fdf..dc5e9a67bdb65 100644
--- a/pandas/tests/test_config.py
+++ b/pandas/tests/test_config.py
@@ -59,6 +59,7 @@ def test_register_option(self):
 
         # no python keywords
         self.assertRaises(ValueError, self.cf.register_option, 'for', 0)
+        self.assertRaises(ValueError, self.cf.register_option, 'a.for.b', 0)
         # must be valid identifier (ensure attribute access works)
         self.assertRaises(ValueError, self.cf.register_option,
                           'Oh my Goddess!', 0)