diff -r bff88c866886 Lib/test/test_warnings.py
--- a/Lib/test/test_warnings.py	Thu Apr 09 10:27:25 2015 +0200
+++ b/Lib/test/test_warnings.py	Tue Apr 14 09:11:34 2015 +0300
@@ -247,6 +247,25 @@
             self.assertEqual(str(w[-1].message), text)
             self.assertTrue(w[-1].category is UserWarning)
 
+    def test_duplicate_filters(self):
+        with original_warnings.catch_warnings(module=self.module):
+            initial_len = len(self.module.filters)
+            self.module.filterwarnings("error", category=UserWarning)
+            self.assertEqual(len(self.module.filters), initial_len + 1)
+            self.module.filterwarnings("ignore", category=UserWarning)
+            self.module.filterwarnings("error", category=UserWarning)
+            self.assertEqual(len(self.module.filters), initial_len + 2, "filterwarnings inserted duplicate filter")
+            self.assertEqual(self.module.filters[0][0], 'error', "filterwarnings did not promote filter to the beginning of list")
+
+        with original_warnings.catch_warnings(module=self.module):
+            initial_len = len(self.module.filters)
+            self.module.simplefilter("error", category=UserWarning)
+            self.assertEqual(len(self.module.filters), initial_len + 1)
+            self.module.simplefilter("ignore", category=UserWarning)
+            self.module.simplefilter("error", category=UserWarning)
+            self.assertEqual(len(self.module.filters), initial_len + 2, "simplefilter inserted duplicate filter")
+            self.assertEqual(self.module.filters[0][0], 'error', "simplefilter did not promote filter to the beginning of list")
+
 class CFilterTests(FilterTests, unittest.TestCase):
     module = c_warnings
 
@@ -456,20 +475,20 @@
         self.assertIn('category must be a Warning subclass, not ',
                       str(cm.exception))
 
-        with original_warnings.catch_warnings(module=self.module):
+        with original_warnings.catch_warnings(module=self.module, record=True) as warns:
             self.module.resetwarnings()
             self.module.filterwarnings('default')
-            with self.assertWarns(MyWarningClass) as cm:
-                self.module.warn('good warning category', MyWarningClass)
-            self.assertEqual('good warning category', str(cm.warning))
 
-            with self.assertWarns(UserWarning) as cm:
-                self.module.warn('good warning category', None)
-            self.assertEqual('good warning category', str(cm.warning))
+            self.module.warn('good warning category', MyWarningClass)
+            self.assertIsInstance(warns[-1].message, MyWarningClass)
+            self.assertEqual('good warning category', str(warns[-1].message))
 
-            with self.assertWarns(MyWarningClass) as cm:
-                self.module.warn('good warning category', MyWarningClass)
-            self.assertIsInstance(cm.warning, Warning)
+            self.module.warn('good warning category', None)
+            self.assertIsInstance(warns[-1].message, UserWarning)
+            self.assertEqual('good warning category', str(warns[-1].message))
+
+            self.module.warn('good warning category', MyWarningClass)
+            self.assertIsInstance(warns[-1].message, Warning)
 
 class CWarnTests(WarnTests, unittest.TestCase):
     module = c_warnings
diff -r bff88c866886 Lib/warnings.py
--- a/Lib/warnings.py	Thu Apr 09 10:27:25 2015 +0200
+++ b/Lib/warnings.py	Tue Apr 14 09:11:34 2015 +0300
@@ -52,6 +52,12 @@
            "lineno must be an int >= 0"
     item = (action, re.compile(message, re.I), category,
             re.compile(module), lineno)
+
+    # Remove possible duplicate filters, so new one will be placed in correct place    
+    try:
+        filters.remove(item)
+    except ValueError:
+        pass
     if append:
         filters.append(item)
     else:
@@ -73,6 +79,12 @@
     assert isinstance(lineno, int) and lineno >= 0, \
            "lineno must be an int >= 0"
     item = (action, None, category, None, lineno)
+
+    # Remove possible duplicate filters, so new one will be placed in correct place
+    try:
+        filters.remove(item)
+    except ValueError:
+        pass
     if append:
         filters.append(item)
     else: