--- Lib/ConfigParser.py
+++ Lib/ConfigParser.py
@@ -94,6 +94,7 @@
     _default_dict = dict
 
 import re
+import string
 
 __all__ = ["NoSectionError", "DuplicateSectionError", "NoOptionError",
            "InterpolationError", "InterpolationDepthError",
@@ -106,6 +107,14 @@
 
 MAX_INTERPOLATION_DEPTH = 10
 
+_lower_map = string.maketrans(string.ascii_uppercase, string.ascii_lowercase)
+
+def _lower(value):
+    if isinstance(value, str):
+        return value.translate(_lower_map)
+    else:
+        return value.lower()
+
 
 
 # exception classes
@@ -257,7 +266,7 @@
         already exists. Raise ValueError if name is DEFAULT or any of it's
         case-insensitive variants.
         """
-        if section.lower() == "default":
+        if _lower(section) == "default":
             raise ValueError, 'Invalid section name: %s' % section
 
         if section in self._sections:
@@ -366,12 +375,12 @@
 
     def getboolean(self, section, option):
         v = self.get(section, option)
-        if v.lower() not in self._boolean_states:
+        if _lower(v) not in self._boolean_states:
             raise ValueError, 'Not a boolean: %s' % v
-        return self._boolean_states[v.lower()]
+        return self._boolean_states[_lower(v)]
 
     def optionxform(self, optionstr):
-        return optionstr.lower()
+        return _lower(optionstr)
 
     def has_option(self, section, option):
         """Check for the existence of a given option in a given section."""
@@ -483,7 +492,7 @@
             # comment or blank line?
             if line.strip() == '' or line[0] in '#;':
                 continue
-            if line.split(None, 1)[0].lower() == 'rem' and line[0] in "rR":
+            if _lower(line.split(None, 1)[0]) == 'rem' and line[0] in "rR":
                 # no leading whitespace
                 continue
             # continuation line?