diff -r 3fba718e46e5 Lib/test/test_cmath.py
--- a/Lib/test/test_cmath.py	Sat Aug 18 09:50:32 2012 +0300
+++ b/Lib/test/test_cmath.py	Sat Aug 18 10:20:25 2012 +0100
@@ -519,15 +519,11 @@
     # of zero, then atan and atanh will also have difficulties with
     # the sign of complex zeros.
     @requires_IEEE_754
-    @unittest.skipIf(sysconfig.get_config_var('LOG1P_DROPS_ZERO_SIGN'),
-                     "system log1p() function doesn't preserve the sign")
     def testAtanSign(self):
         for z in complex_zeros:
             self.assertComplexIdentical(cmath.atan(z), z)
 
     @requires_IEEE_754
-    @unittest.skipIf(sysconfig.get_config_var('LOG1P_DROPS_ZERO_SIGN'),
-                     "system log1p() function doesn't preserve the sign")
     def testAtanhSign(self):
         for z in complex_zeros:
             self.assertComplexIdentical(cmath.atanh(z), z)
diff -r 3fba718e46e5 Modules/_math.c
--- a/Modules/_math.c	Sat Aug 18 09:50:32 2012 +0300
+++ b/Modules/_math.c	Sat Aug 18 10:20:25 2012 +0100
@@ -189,6 +189,27 @@
    significant loss of precision that arises from direct evaluation when x is
    small. */
 
+#ifdef HAVE_LOG1P
+
+double
+_Py_log1p(double x)
+{
+    /* Some platforms supply a log1p function but don't respect the sign of
+       zero:  log1p(-0.0) gives 0.0 instead of the correct result of -0.0.
+
+       To save fiddling with configure tests and platform checks, we handle the
+       special case of zero input directly on all platforms.
+    */
+    if (x == 0.0) {
+        return x;
+    }
+    else {
+        return log1p(x);
+    }
+}
+
+#else
+
 double
 _Py_log1p(double x)
 {
@@ -230,3 +251,5 @@
         return log(1.+x);
     }
 }
+
+#endif /* ifdef HAVE_LOG1P */
diff -r 3fba718e46e5 Modules/_math.h
--- a/Modules/_math.h	Sat Aug 18 09:50:32 2012 +0300
+++ b/Modules/_math.h	Sat Aug 18 10:20:25 2012 +0100
@@ -36,10 +36,6 @@
 #define m_expm1 _Py_expm1
 #endif
 
-#ifdef HAVE_LOG1P
-#define m_log1p log1p
-#else
-/* if the system doesn't have log1p, use the substitute
-   function defined in Modules/_math.c. */
+/* Use the substitute from _math.c on all platforms:
+   it includes workarounds for buggy handling of zeros. */
 #define m_log1p _Py_log1p
-#endif