diff --git a/Lib/test/test_warnings.py b/Lib/test/test_warnings.py
index 43b3b9c..0f2e089 100644
--- a/Lib/test/test_warnings.py
+++ b/Lib/test/test_warnings.py
@@ -92,6 +92,16 @@
             self.assertRaises(UserWarning, self.module.warn,
                                 "FilterTests.test_error")
 
+    def test_error_after_default(self):
+        with original_warnings.catch_warnings(module=self.module) as w:
+            self.module.resetwarnings()
+            message = "FilterTests.test_ignore_after_default"
+            def f():
+                self.module.warn(message, UserWarning)
+            f()
+            self.module.filterwarnings("error", category=UserWarning)
+            self.assertRaises(UserWarning, f)
+
     def test_ignore(self):
         with original_warnings.catch_warnings(record=True,
                 module=self.module) as w:
@@ -100,6 +110,19 @@
             self.module.warn("FilterTests.test_ignore", UserWarning)
             self.assertEqual(len(w), 0)
 
+    def test_ignore_after_default(self):
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
+            self.module.resetwarnings()
+            message = "FilterTests.test_ignore_after_default"
+            def f():
+                self.module.warn(message, UserWarning)
+            f()
+            self.module.filterwarnings("ignore", category=UserWarning)
+            f()
+            f()
+            self.assertEqual(len(w), 1)
+
     def test_always(self):
         with original_warnings.catch_warnings(record=True,
                 module=self.module) as w:
@@ -111,6 +134,26 @@
             self.module.warn(message, UserWarning)
             self.assertTrue(w[-1].message, message)
 
+    def test_always_after_default(self):
+        with original_warnings.catch_warnings(record=True,
+                module=self.module) as w:
+            self.module.resetwarnings()
+            message = "FilterTests.test_always_after_ignore"
+            def f():
+                self.module.warn(message, UserWarning)
+            f()
+            self.assertEqual(len(w), 1)
+            self.assertEqual(w[-1].message.args[0], message)
+            f()
+            self.assertEqual(len(w), 1)
+            self.module.filterwarnings("always", category=UserWarning)
+            f()
+            self.assertEqual(len(w), 2)
+            self.assertEqual(w[-1].message.args[0], message)
+            f()
+            self.assertEqual(len(w), 3)
+            self.assertEqual(w[-1].message.args[0], message)
+
     def test_default(self):
         with original_warnings.catch_warnings(record=True,
                 module=self.module) as w:
@@ -506,7 +549,9 @@
                                             registry=registry)
                 self.assertEqual(w[-1].message, message)
                 self.assertEqual(len(w), 1)
-                self.assertEqual(len(registry), 1)
+                # One actual registry key plus the "version" key
+                self.assertEqual(len(registry), 2)
+                self.assertIn("version", registry)
                 del w[:]
                 # Test removal.
                 del self.module.defaultaction
@@ -516,7 +561,7 @@
                                             registry=registry)
                 self.assertEqual(w[-1].message, message)
                 self.assertEqual(len(w), 1)
-                self.assertEqual(len(registry), 1)
+                self.assertEqual(len(registry), 2)
                 del w[:]
                 # Test setting.
                 self.module.defaultaction = "ignore"
diff --git a/Lib/warnings.py b/Lib/warnings.py
index eeeba65..5d5c9a9 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -53,6 +53,7 @@
         filters.append(item)
     else:
         filters.insert(0, item)
+    _filters_mutated()
 
 def simplefilter(action, category=Warning, lineno=0, append=False):
     """Insert a simple entry into the list of warnings filters (at the front).
@@ -73,10 +74,12 @@
         filters.append(item)
     else:
         filters.insert(0, item)
+    _filters_mutated()
 
 def resetwarnings():
     """Clear the list of warning filters, so that no filters are active."""
     filters[:] = []
+    _filters_mutated()
 
 class _OptionError(Exception):
     """Exception used by option processing helpers."""
@@ -204,6 +207,9 @@
             module = module[:-3] # XXX What about leading pathname?
     if registry is None:
         registry = {}
+    if registry.get('version', 0) != _filters_version:
+        registry.clear()
+        registry['version'] = _filters_version
     if isinstance(message, Warning):
         text = str(message)
         category = message.__class__
@@ -329,6 +335,7 @@
         self._entered = True
         self._filters = self._module.filters
         self._module.filters = self._filters[:]
+        self._module._filters_mutated()
         self._showwarning = self._module.showwarning
         if self._record:
             log = []
@@ -343,6 +350,7 @@
         if not self._entered:
             raise RuntimeError("Cannot exit %r without entering first" % self)
         self._module.filters = self._filters
+        self._module._filters_mutated()
         self._module.showwarning = self._showwarning
 
 
@@ -357,15 +365,22 @@
 _warnings_defaults = False
 try:
     from _warnings import (filters, _defaultaction, _onceregistry,
-                            warn, warn_explicit)
+                           warn, warn_explicit, _filters_mutated)
     defaultaction = _defaultaction
     onceregistry = _onceregistry
     _warnings_defaults = True
+
 except ImportError:
     filters = []
     defaultaction = "default"
     onceregistry = {}
 
+    _filters_version = 1
+
+    def _filters_mutated():
+        global _filters_version
+        _filters_version += 1
+
 
 # Module initialization
 _processoptions(sys.warnoptions)