diff -r ebb23744a36c Lib/enum.py
--- a/Lib/enum.py	Wed Aug 31 23:00:32 2016 -0700
+++ b/Lib/enum.py	Thu Sep 01 11:02:37 2016 +0200
@@ -785,12 +785,7 @@ class IntFlags(int, Flags):
 
 def _high_bit(value):
     """return the highest bit set in value"""
-    bit = 0
-    while 'looking for the highest bit':
-        limit = 2 ** bit
-        if limit > value:
-            return bit - 1
-        bit += 1
+    return value.bit_length() - 1
 
 def unique(enumeration):
     """Class decorator for enumerations ensuring unique member values."""