diff --git a/Lib/rational.py b/Lib/rational.py
index 90abe62..40b9163 100755
--- a/Lib/rational.py
+++ b/Lib/rational.py
@@ -14,7 +14,7 @@
 RationalAbc = numbers.Rational
 
 
-def _gcd(a, b):
+def _gcd(a, b):                     # XXX This is a useful function. Consider making it public.
     """Calculate the Greatest Common Divisor.
 
     Unless b==0, the result will have the same sign as b (so that when