diff -r 0909f73cfa3a Lib/unittest/case.py
--- a/Lib/unittest/case.py	Sat Mar 08 16:36:37 2014 +1000
+++ b/Lib/unittest/case.py	Tue Mar 11 20:40:46 2014 -0300
@@ -143,8 +143,10 @@
                 self.obj_name = str(callable_obj)
         else:
             self.obj_name = None
-        if isinstance(expected_regex, (bytes, str)):
+                    
+        if expected_regex is not None:
             expected_regex = re.compile(expected_regex)
+
         self.expected_regex = expected_regex
         self.msg = None
 
diff -r 0909f73cfa3a Lib/unittest/test/test_case.py
--- a/Lib/unittest/test/test_case.py	Sat Mar 08 16:36:37 2014 +1000
+++ b/Lib/unittest/test/test_case.py	Tue Mar 11 20:40:46 2014 -0300
@@ -1126,6 +1126,26 @@
                 self.assertRaisesRegex, Exception, 'x',
                 lambda: None)
 
+    def testAssertRaisesRegexInvalidRegex(self):
+        class ExceptionMock(Exception):
+            pass
+        
+        def Stub():
+            raise ExceptionMock('We expect')
+
+        self.assertRaises(TypeError, self.assertRaisesRegex, ExceptionMock, 123456, Stub)
+
+
+    def testAssertWarnsRegexInvalidRegex(self):
+        class WarningMock(Warning):
+            pass
+
+        def Stub():
+            raise WarningMock('We expect')
+        
+
+        self.assertRaises(TypeError, self.assertWarnsRegex, WarningMock, 12345, Stub)
+
     def testAssertRaisesRegexMismatch(self):
         def Stub():
             raise Exception('Unexpected')