--- a/Lib/decimal.py	Thu Aug 02 17:50:06 2012 -0400
+++ b/Lib/decimal.py	Fri Aug 03 19:01:52 2012 +1000
@@ -1601,6 +1601,8 @@
 
     def __float__(self):
         """Float representation."""
+        if self.is_qnan():
+            return _math.copysign(float('nan'), (-1)**self._sign)
         return float(str(self))
 
     def __int__(self):