diff --git a/Lib/email/Charset.py b/Lib/email/Charset.py
index 6a3e3ca..df860c5 100644
--- a/Lib/email/Charset.py
+++ b/Lib/email/Charset.py
@@ -185,8 +185,9 @@
                   this attribute will have the same value as the input_codec.
     """
     def __init__(self, input_charset=DEFAULT_CHARSET):
-        # RFC 2046, $4.1.2 says charsets are not case sensitive
-        input_charset = input_charset.lower()
+        # RFC 2046, $4.1.2 says charsets are not case sensitive.  We coerce to
+        # unicode because its .lower() is locale insensitive.
+        input_charset = unicode(input_charset, 'ascii').lower()
         # Set the input charset after filtering through the aliases
         self.input_charset = ALIASES.get(input_charset, input_charset)
         # We can try to guess which encoding and conversion to use by the