diff -r 8773e59530c2 Lib/test/test_peepholer.py
--- a/Lib/test/test_peepholer.py	Thu Mar 10 15:51:11 2011 -0500
+++ b/Lib/test/test_peepholer.py	Thu Mar 10 16:11:51 2011 -0500
@@ -3,6 +3,7 @@
 import sys
 from io import StringIO
 import unittest
+from math import copysign
 
 def disassemble(func):
     f = StringIO()
@@ -198,6 +199,8 @@
     def test_folding_of_unaryops_on_constants(self):
         for line, elem in (
             ('-0.5', '(-0.5)'),                     # unary negative
+            ('-0.0', '(-0.0)'),                     # -0.0
+            ('-(1.0-1.0)','(-0.0)'),                # -0.0 after folding
             ('~-2', '(1)'),                         # unary invert
             ('+1', '(1)'),                          # unary positive
         ):
@@ -205,6 +208,12 @@
             self.assertIn(elem, asm, asm)
             self.assertNotIn('UNARY_', asm)
 
+        # Check that -0.0 works after marshaling
+        def negzero(): return -(1.0-1.0)
+
+        self.assertNotIn('UNARY_', disassemble(negzero))
+        self.assertTrue(copysign(1.0, negzero()) < 0)
+
         # Verify that unfoldables are skipped
         for line, elem in (
             ('-"abc"', "('abc')"),                  # unary negative
diff -r 8773e59530c2 Python/peephole.c
--- a/Python/peephole.c	Thu Mar 10 15:51:11 2011 -0500
+++ b/Python/peephole.c	Thu Mar 10 16:11:51 2011 -0500
@@ -189,7 +189,7 @@
 static int
 fold_unaryops_on_constants(unsigned char *codestr, PyObject *consts)
 {
-    PyObject *newconst=NULL, *v;
+    PyObject *newconst, *v;
     Py_ssize_t len_consts;
     int opcode;
 
@@ -202,9 +202,7 @@
     opcode = codestr[3];
     switch (opcode) {
         case UNARY_NEGATIVE:
-            /* Preserve the sign of -0.0 */
-            if (PyObject_IsTrue(v) == 1)
-                newconst = PyNumber_Negative(v);
+            newconst = PyNumber_Negative(v);
             break;
         case UNARY_INVERT:
             newconst = PyNumber_Invert(v);