1 files changed, 14 insertions, 1 deletions
diff --git a/Doc/library/decimal.rst b/Doc/library/decimal.rst
index 3c3e613e62e..f6b96b23b8c 100644
--- a/Doc/library/decimal.rst
+++ b/Doc/library/decimal.rst
@@ -86,7 +86,7 @@ reset them before monitoring a calculation.
      Specification <http://www2.hursley.ibm.com/decimal/decarith.html>`_.
 
    * IEEE standard 854-1987, `Unofficial IEEE 854 Text
-     <http://www.cs.berkeley.edu/~ejr/projects/754/private/drafts/854-1987/dir.html>`_.
+     <http://754r.ucbtest.org/standards/854.pdf>`_.
 
 .. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
@@ -1238,6 +1238,19 @@ A variant is :const:`sNaN` which signals rather than remaining quiet after every
 operation.  This is a useful return value when an invalid result needs to
 interrupt a calculation for special handling.
 
+The behavior of Python's comparison operators can be a little surprising where a
+:const:`NaN` is involved.  A test for equality where one of the operands is a
+quiet or signaling :const:`NaN` always returns :const:`False` (even when doing
+``Decimal('NaN')==Decimal('NaN')``), while a test for inequality always returns
+:const:`True`.  An attempt to compare two Decimals using any of the ``<``,
+``<=``, ``>`` or ``>=`` operators will raise the :exc:`InvalidOperation` signal
+if either operand is a :const:`NaN`, and return :const:`False` if this signal is
+trapped.  Note that the General Decimal Arithmetic specification does not
+specify the behavior of direct comparisons; these rules for comparisons
+involving a :const:`NaN` were taken from the IEEE 854 standard (see Table 3 in
+section 5.7).  To ensure strict standards-compliance, use the :meth:`compare`
+and :meth:`compare-signal` methods instead.
+
 The signed zeros can result from calculations that underflow. They keep the sign
 that would have resulted if the calculation had been carried out to greater
 precision.  Since their magnitude is zero, both positive and negative zeros are