@@ -108,6 +108,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="arraytest.cs" />
+    <Compile Include="callbacktest.cs" />
     <Compile Include="classtest.cs" />
     <Compile Include="constructortests.cs" />
     <Compile Include="conversiontest.cs" />
@@ -127,6 +128,7 @@
     <Compile Include="subclasstest.cs" />
   </ItemGroup>
   <ItemGroup>
+    <Reference Include="Microsoft.CSharp" />
     <Reference Include="System" />
     <Reference Include="System.Core">
       <RequiredTargetFramework>3.5</RequiredTargetFramework>
 
@@ -0,0 +1,31 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Python.Test
+{
+    //========================================================================
+    // Tests callbacks into python code.
+    //========================================================================
+
+    public class CallbackTest
+    {
+        public string Call_simpleDefaultArg_WithNull(string moduleName)
+        {
+            using (Runtime.Py.GIL())
+            {
+                dynamic module = Runtime.Py.Import(moduleName);
+                return module.simpleDefaultArg(null);
+            }
+        }
+        public string Call_simpleDefaultArg_WithEmptyArgs(string moduleName)
+        {
+            using (Runtime.Py.GIL())
+            {
+                dynamic module = Runtime.Py.Import(moduleName);
+                return module.simpleDefaultArg();
+            }
+        }
+    }
+}
@@ -3,8 +3,10 @@
 __all__ = ['test_suite']
 
 from .test_import import test_suite as import_tests
+from .test_callback import test_suite as callback_tests
 
 def test_suite():
     suite = unittest.TestSuite()
     suite.addTests((import_tests(),))
+    suite.addTests((callback_tests(),))
     return suite
@@ -0,0 +1,30 @@
+import unittest, sys
+import clr
+
+this_module = sys.modules[__name__]
+clr.AddReference("Python.Test")
+import Python.Test as Test
+from Python.Test import CallbackTest
+test_instance = CallbackTest()
+
+def simpleDefaultArg(arg = 'test'):
+    return arg
+
+class CallbackTests(unittest.TestCase):
+    """Test that callbacks from C# into python work."""
+
+    def testDefaultForNull(self):
+        """Test that C# can use null for an optional python argument"""
+        retVal = test_instance.Call_simpleDefaultArg_WithNull(__name__)
+        pythonRetVal = simpleDefaultArg(None)
+        self.assertEquals(retVal, pythonRetVal)
+
+    def testDefaultForNone(self):
+        """Test that C# can use no argument for an optional python argument"""
+        retVal = test_instance.Call_simpleDefaultArg_WithEmptyArgs(__name__)
+        pythonRetVal = simpleDefaultArg()
+        self.assertEquals(retVal, pythonRetVal)
+
+def test_suite():
+    return unittest.makeSuite(CallbackTests)
+