Index: Lib/test/pickletester.py
===================================================================
--- Lib/test/pickletester.py	(revision 82823)
+++ Lib/test/pickletester.py	(working copy)
@@ -3,6 +3,7 @@
 import cPickle
 import StringIO
 import pickletools
+import math
 import copy_reg
 
 from test.test_support import TestFailed, have_unicode, TESTFN, \
@@ -548,7 +549,8 @@
 
     def test_float(self):
         test_values = [0.0, 4.94e-324, 1e-310, 7e-308, 6.626e-34, 0.1, 0.5,
-                       3.14, 263.44582062374053, 6.022e23, 1e30]
+                       3.14, 263.44582062374053, 6.022e23, 1e30,
+                       float('inf')]
         test_values = test_values + [-x for x in test_values]
         for proto in protocols:
             for value in test_values:
@@ -556,6 +558,13 @@
                 got = self.loads(pickle)
                 self.assertEqual(value, got)
 
+    def test_float_nan(self):
+        nan = float('nan')
+        for proto in protocols:
+            pickle = self.dumps(nan, proto)
+            got = self.loads(pickle)
+            self.assertTrue(math.isnan, got)
+
     @run_with_locale('LC_ALL', 'de_DE', 'fr_FR')
     def test_float_format(self):
         # make sure that floats are formatted locale independent
Index: Modules/cPickle.c
===================================================================
--- Modules/cPickle.c	(revision 82823)
+++ Modules/cPickle.c	(working copy)
@@ -1172,7 +1172,7 @@
     else {
         char c_str[250];
         c_str[0] = FLOAT;
-        PyOS_ascii_formatd(c_str + 1, sizeof(c_str) - 2, "%.17g", x);
+	PyFloat_AsReprString(c_str + 1, (PyFloatObject *)args);
         /* Extend the formatted string with a newline character */
         strcat(c_str, "\n");