diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index 401fc1e..da8a0e9 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -124,6 +124,59 @@
         self.ftest('atan2(1, 1)', math.atan2(1, 1), math.pi/4)
         self.ftest('atan2(1, 0)', math.atan2(1, 0), math.pi/2)
 
+        # math.atan2(0, x)
+        self.ftest('atan2(0., -inf)', math.atan2(0., NINF), math.pi)
+        self.ftest('atan2(0., -2.3)', math.atan2(0., -2.3), math.pi)
+        self.ftest('atan2(0., -0.)', math.atan2(0., -0.), math.pi)
+        self.assertEqual(math.atan2(0., 0.), 0.)
+        self.assertEqual(math.atan2(0., 2.3), 0.)
+        self.assertEqual(math.atan2(0., INF), 0.)
+        self.assert_(math.isnan(math.atan2(0., NAN)))
+        # math.atan2(-0, x)
+        self.ftest('atan2(-0., -inf)', math.atan2(-0., NINF), -math.pi)
+        self.ftest('atan2(-0., -2.3)', math.atan2(-0., -2.3), -math.pi)
+        self.ftest('atan2(-0., -0.)', math.atan2(-0., -0.), -math.pi)
+        self.assertEqual(math.atan2(-0., 0.), -0.)
+        self.assertEqual(math.atan2(-0., 2.3), -0.)
+        self.assertEqual(math.atan2(-0., INF), -0.)
+        self.assert_(math.isnan(math.atan2(-0., NAN)))
+        # math.atan2(INF, x)
+        self.ftest('atan2(inf, -inf)', math.atan2(INF, NINF), math.pi*3/4)
+        self.ftest('atan2(inf, -2.3)', math.atan2(INF, -2.3), math.pi/2)
+        self.ftest('atan2(inf, -0.)', math.atan2(INF, -0.0), math.pi/2)
+        self.ftest('atan2(inf, 0.)', math.atan2(INF, 0.0), math.pi/2)
+        self.ftest('atan2(inf, 2.3)', math.atan2(INF, 2.3), math.pi/2)
+        self.ftest('atan2(inf, inf)', math.atan2(INF, INF), math.pi/4)
+        self.assert_(math.isnan(math.atan2(INF, NAN)))
+        # math.atan2(NINF, x)
+        self.ftest('atan2(-inf, -inf)', math.atan2(NINF, NINF), -math.pi*3/4)
+        self.ftest('atan2(-inf, -2.3)', math.atan2(NINF, -2.3), -math.pi/2)
+        self.ftest('atan2(-inf, -0.)', math.atan2(NINF, -0.0), -math.pi/2)
+        self.ftest('atan2(-inf, 0.)', math.atan2(NINF, 0.0), -math.pi/2)
+        self.ftest('atan2(-inf, 2.3)', math.atan2(NINF, 2.3), -math.pi/2)
+        self.ftest('atan2(-inf, inf)', math.atan2(NINF, INF), -math.pi/4)
+        self.assert_(math.isnan(math.atan2(NINF, NAN)))
+        # math.atan2(+finite, x)
+        self.ftest('atan2(2.3, -inf)', math.atan2(2.3, NINF), math.pi)
+        self.ftest('atan2(2.3, -0.)', math.atan2(2.3, -0.), math.pi/2)
+        self.ftest('atan2(2.3, 0.)', math.atan2(2.3, 0.), math.pi/2)
+        self.assertEqual(math.atan2(2.3, INF), 0.)
+        self.assert_(math.isnan(math.atan2(2.3, NAN)))
+        # math.atan2(-finite, x)
+        self.ftest('atan2(-2.3, -inf)', math.atan2(-2.3, NINF), -math.pi)
+        self.ftest('atan2(-2.3, -0.)', math.atan2(-2.3, -0.), -math.pi/2)
+        self.ftest('atan2(-2.3, 0.)', math.atan2(-2.3, 0.), -math.pi/2)
+        self.assertEqual(math.atan2(-2.3, INF), -0.)
+        self.assert_(math.isnan(math.atan2(-2.3, NAN)))
+        # math.atan2(NAN, x)
+        self.assert_(math.isnan(math.atan2(NAN, NINF)))
+        self.assert_(math.isnan(math.atan2(NAN, -2.3)))
+        self.assert_(math.isnan(math.atan2(NAN, -0.)))
+        self.assert_(math.isnan(math.atan2(NAN, 0.)))
+        self.assert_(math.isnan(math.atan2(NAN, 2.3)))
+        self.assert_(math.isnan(math.atan2(NAN, INF)))
+        self.assert_(math.isnan(math.atan2(NAN, NAN)))
+
     def testCeil(self):
         self.assertRaises(TypeError, math.ceil)
         self.assertEquals(int, type(math.ceil(0.5)))
@@ -575,6 +628,11 @@
         self.ftest('tanh(inf)', math.tanh(INF), 1)
         self.ftest('tanh(-inf)', math.tanh(NINF), -1)
         self.assert_(math.isnan(math.tanh(NAN)))
+        # check that tanh(-0.) == -0. on IEEE 754 systems
+        if float.__getformat__("double").startswith("IEEE"):
+            self.assertEqual(math.tanh(-0.), -0.)
+            self.assertEqual(math.copysign(1., math.tanh(-0.)),
+                             math.copysign(1., -0.))
 
     def test_trunc(self):
         self.assertEqual(math.trunc(1), 1)
diff --git a/Lib/test/test_pkgutil.py b/Lib/test/test_pkgutil.py
index c9ec060..dfd2430 100644
--- a/Lib/test/test_pkgutil.py
+++ b/Lib/test/test_pkgutil.py
@@ -122,6 +122,9 @@
 
 def test_main():
     run_unittest(PkgutilTests, PkgutilPEP302Tests)
+    # this is necessary if test is run repeated (like when finding leaks)
+    import zipimport
+    zipimport._zip_directory_cache.clear()
 
 if __name__ == '__main__':
     test_main()
diff --git a/Modules/cmathmodule.c b/Modules/cmathmodule.c
index 347f88d..d6d1f27 100644
--- a/Modules/cmathmodule.c
+++ b/Modules/cmathmodule.c
@@ -264,7 +264,8 @@
 	return r;
 }
 
-/* Windows screws up atan2 for inf and nan */
+/* Windows screws up atan2 for inf and nan, and alpha Tru64 5.1 doesn't follow
+   C99 for atan2(0., 0.). */
 static double
 c_atan2(Py_complex z)
 {
@@ -282,6 +283,14 @@
 		/* atan2(+-inf, x) == +-pi/2 for finite x */
 		return copysign(0.5*Py_MATH_PI, z.imag);
 	}
+	if (Py_IS_INFINITY(z.real) || z.imag == 0.) {
+		if (copysign(1., z.real) == 1.)
+			/* atan2(+-y, +inf) = atan2(+-0, +x) = +-0. */
+			return copysign(0., z.imag);
+		else
+			/* atan2(+-y, -inf) = atan2(+-0., -x) = +-pi. */
+			return copysign(Py_MATH_PI, z.imag);
+	}
 	return atan2(z.imag, z.real);
 }
 
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 19ed1b1..3cf1133 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -96,6 +96,42 @@
 }
 
 /*
+   wrapper for atan2 that deals directly with special cases before
+   delegating to the platform libm for the remaining cases.  This
+   is necessary to get consistent behaviour across platforms.
+   Windows, FreeBSD and alpha Tru64 are amongst platforms that don't
+   always follow C99.
+*/
+
+static double
+m_atan2(double y, double x)
+{
+	if (Py_IS_NAN(x) || Py_IS_NAN(y))
+		return Py_NAN;
+	if (Py_IS_INFINITY(y)) {
+		if (Py_IS_INFINITY(x)) {
+			if (copysign(1., x) == 1.)
+				/* atan2(+-inf, +inf) == +-pi/4 */
+				return copysign(0.25*Py_MATH_PI, y);
+			else
+				/* atan2(+-inf, -inf) == +-pi*3/4 */
+				return copysign(0.75*Py_MATH_PI, y);
+		}
+		/* atan2(+-inf, x) == +-pi/2 for finite x */
+		return copysign(0.5*Py_MATH_PI, y);
+	}
+	if (Py_IS_INFINITY(x) || y == 0.) {
+		if (copysign(1., x) == 1.)
+			/* atan2(+-y, +inf) = atan2(+-0, +x) = +-0. */
+			return copysign(0., y);
+		else
+			/* atan2(+-y, -inf) = atan2(+-0., -x) = +-pi. */
+			return copysign(Py_MATH_PI, y);
+	}
+	return atan2(y, x);
+}
+
+/*
    math_1 is used to wrap a libm function f that takes a double
    arguments and returns a double.
 
@@ -250,7 +286,7 @@
       "asinh(x)\n\nReturn the hyperbolic arc sine (measured in radians) of x.")
 FUNC1(atan, atan, 0,
       "atan(x)\n\nReturn the arc tangent (measured in radians) of x.")
-FUNC2(atan2, atan2,
+FUNC2(atan2, m_atan2,
       "atan2(y, x)\n\nReturn the arc tangent (measured in radians) of y/x.\n"
       "Unlike atan(y/x), the signs of both x and y are considered.")
 FUNC1(atanh, atanh, 0,