diff --git a/env.py b/env.py
index 4a50f13..9120657 100644
--- a/env.py
+++ b/env.py
@@ -56,13 +56,13 @@ def prefix(prefix):
 
 def map(**kwargs):
     """Returns a dictionary of the given keyword arguments mapped to their
-    values from the environment.
+    values from the environment, with input and output keys lower cased.
     """
 
     d = {}
     e = lower_dict(environ.copy())
 
     for k, v in kwargs.iteritems():
-        d[k] = e.get(v)
+        d[k.lower()] = e.get(v.lower())
 
     return d