diff -r 18882c93f4bd Lib/numbers.py
--- a/Lib/numbers.py	Mon Apr 27 13:53:54 2015 +0300
+++ b/Lib/numbers.py	Mon Apr 27 14:49:45 2015 +0200
@@ -281,14 +281,18 @@
 
     # Concrete implementation of Real's conversion to float.
     def __float__(self):
-        """float(self) = self.numerator / self.denominator
+        """float(self) = float(self.numerator / self.denominator)
 
-        It's important that this conversion use the integer's "true"
-        division rather than casting one side to float before dividing
-        so that ratios of huge integers convert without overflowing.
+        It's important that this conversion use "true" division of the
+        numerator and denominator rather than casting one side to float
+        before dividing so that ratios of huge integers convert without
+        overflowing.
+        If the result of the division is another Rational instance, care
+        should be taken to avoid infinite recursion, e.g., by overriding
+        __float__ in the returned type.
 
         """
-        return self.numerator / self.denominator
+        return float(self.numerator / self.denominator)
 
 
 class Integral(Rational):