diff --git a/Lib/test/test_cmath.py b/Lib/test/test_cmath.py
index 668f27c8a..7bf438dbb 100644
--- a/Lib/test/test_cmath.py
+++ b/Lib/test/test_cmath.py
@@ -50,14 +50,18 @@ complex_nans = [complex(x, y) for x, y in [
         ]]
 
 class CMathTests(unittest.TestCase):
+    # TODO: RUSTPYTHON:
+    # Uncomment when functions have been added. Temporarily 
+    # commented out to allow incremented addition of functions.
+    #
     # list of all functions in cmath
-    test_functions = [getattr(cmath, fname) for fname in [
-            'acos', 'acosh', 'asin', 'asinh', 'atan', 'atanh',
-            'cos', 'cosh', 'exp', 'log', 'log10', 'sin', 'sinh',
-            'sqrt', 'tan', 'tanh']]
+    # test_functions = [getattr(cmath, fname) for fname in [
+    #        'acos', 'acosh', 'asin', 'asinh', 'atan', 'atanh',
+    #        'cos', 'cosh', 'exp', 'log', 'log10', 'sin', 'sinh',
+    #        'sqrt', 'tan', 'tanh']]
     # test first and second arguments independently for 2-argument log
-    test_functions.append(lambda x : cmath.log(x, 1729. + 0j))
-    test_functions.append(lambda x : cmath.log(14.-27j, x))
+    # test_functions.append(lambda x : cmath.log(x, 1729. + 0j))
+    # test_functions.append(lambda x : cmath.log(14.-27j, x))
 
     def setUp(self):
         self.test_values = open(test_file)
@@ -156,6 +160,8 @@ class CMathTests(unittest.TestCase):
         self.assertAlmostEqual(cmath.e, e_expected, places=9,
             msg="cmath.e is {}; should be {}".format(cmath.e, e_expected))
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     def test_infinity_and_nan_constants(self):
         self.assertEqual(cmath.inf.real, math.inf)
         self.assertEqual(cmath.inf.imag, 0.0)
@@ -173,6 +179,8 @@ class CMathTests(unittest.TestCase):
         self.assertEqual(repr(cmath.nan), "nan")
         self.assertEqual(repr(cmath.nanj), "nanj")
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     def test_user_object(self):
         # Test automatic calling of __complex__ and __float__ by cmath
         # functions
@@ -271,6 +279,8 @@ class CMathTests(unittest.TestCase):
             self.assertRaises(SomeException, f, MyComplexException())
             self.assertRaises(SomeException, f, MyComplexExceptionOS())
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     def test_input_type(self):
         # ints should be acceptable inputs to all cmath
         # functions, by virtue of providing a __float__ method
@@ -283,6 +293,8 @@ class CMathTests(unittest.TestCase):
             for arg in ["a", "long_string", "0", "1j", ""]:
                 self.assertRaises(TypeError, f, arg)
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     def test_cmath_matches_math(self):
         # check that corresponding cmath and math functions are equal
         # for floats in the appropriate range
@@ -331,6 +343,8 @@ class CMathTests(unittest.TestCase):
                 self.rAssertAlmostEqual(math.log(v, base), z.real)
                 self.assertEqual(0., z.imag)
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     @requires_IEEE_754
     def test_specific_values(self):
         # Some tests need to be skipped on ancient OS X versions.
@@ -526,7 +540,8 @@ class CMathTests(unittest.TestCase):
         self.assertEqual(abs(complex(INF, NAN)), INF)
         self.assertTrue(math.isnan(abs(complex(NAN, NAN))))
 
-
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     @requires_IEEE_754
     def test_abs_overflows(self):
         # result overflows
@@ -575,6 +590,8 @@ class CMathTests(unittest.TestCase):
         self.assertTrue(cmath.isinf(complex(NAN, INF)))
         self.assertTrue(cmath.isinf(complex(INF, NAN)))
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     @requires_IEEE_754
     def testTanhSign(self):
         for z in complex_zeros:
@@ -584,11 +601,15 @@ class CMathTests(unittest.TestCase):
     # log1p function; If that system function doesn't respect the sign
     # of zero, then atan and atanh will also have difficulties with
     # the sign of complex zeros.
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     @requires_IEEE_754
     def testAtanSign(self):
         for z in complex_zeros:
             self.assertComplexIdentical(cmath.atan(z), z)
 
+    # TODO: RUSTPYTHON
+    @unittest.expectedFailure
     @requires_IEEE_754
     def testAtanhSign(self):
         for z in complex_zeros:
diff --git a/vm/src/stdlib/cmath.rs b/vm/src/stdlib/cmath.rs
index dceceb9c3..5de8b5eb6 100644
--- a/vm/src/stdlib/cmath.rs
+++ b/vm/src/stdlib/cmath.rs
@@ -105,15 +105,8 @@ mod cmath {
     fn isclose(args: IsCloseArgs, vm: &VirtualMachine) -> PyResult<bool> {
         let a = args.a.to_complex();
         let b = args.b.to_complex();
-        let rel_tol = match args.rel_tol {
-            OptionalArg::Missing => 1e-09,
-            OptionalArg::Present(ref value) => value.to_f64(),
-        };
-
-        let abs_tol = match args.abs_tol {
-            OptionalArg::Missing => 0.0,
-            OptionalArg::Present(ref value) => value.to_f64(),
-        };
+        let rel_tol = args.rel_tol.map_or(1e-09, |value| value.to_f64());
+        let abs_tol = args.abs_tol.map_or(0.0, |value| value.to_f64());
 
         if rel_tol < 0.0 || abs_tol < 0.0 {
             return Err(vm.new_value_error("tolerances must be non-negative".to_owned()));