diff -r 5fd1f8271e8a Lib/test/regrtest.py
--- a/Lib/test/regrtest.py	Wed Aug 13 09:35:21 2014 +0300
+++ b/Lib/test/regrtest.py	Wed Aug 13 17:20:15 2014 +1000
@@ -1363,6 +1363,7 @@
     # This code is hackish and inelegant, but it seems to do the job.
     import copyreg
     import collections.abc
+    import encodings
 
     if not hasattr(sys, 'gettotalrefcount'):
         raise Exception("Tracking reference leaks requires a debug build "
@@ -1378,6 +1379,7 @@
         zdc = None # Run unmodified on platforms without zipimport support
     else:
         zdc = zipimport._zip_directory_cache.copy()
+    codec_cache = encodings._cache.copy()
     abcs = {}
     for abc in [getattr(collections.abc, a) for a in collections.abc.__all__]:
         if not isabstract(abc):
@@ -1394,12 +1396,23 @@
     print("beginning", repcount, "repetitions", file=sys.stderr)
     print(("1234567890"*(repcount//10 + 1))[:repcount], file=sys.stderr)
     sys.stderr.flush()
+    import tracemalloc
     for i in range(repcount):
+        tracemalloc.start(5)
+        trace_before = tracemalloc.take_snapshot()
         indirect_test()
-        alloc_after, rc_after = dash_R_cleanup(fs, ps, pic, zdc, abcs)
+        alloc_after, rc_after = dash_R_cleanup(fs, ps, pic, zdc,
+                                               codec_cache, abcs)
+        trace_after = tracemalloc.take_snapshot()
+        tracemalloc.stop()
+
         sys.stderr.write('.')
         sys.stderr.flush()
         if i >= nwarmup:
+            top_stats = trace_after.compare_to(trace_before, 'traceback')
+            print("[ Top 20 differences ]")
+            for stat in top_stats[:20]:
+                print(stat)
             rc_deltas[i] = rc_after - rc_before
             alloc_deltas[i] = alloc_after - alloc_before
         alloc_before, rc_before = alloc_after, rc_after
@@ -1430,11 +1443,13 @@
             failed = True
     return failed
 
-def dash_R_cleanup(fs, ps, pic, zdc, abcs):
+def dash_R_cleanup(fs, ps, pic, zdc, codec_cache, abcs):
     import gc, copyreg
     import _strptime, linecache
     import urllib.parse, urllib.request, mimetypes, doctest
-    import struct, filecmp, collections.abc
+    import struct, filecmp
+    import encodings
+    import collections.abc
     from distutils.dir_util import _path_created
     from weakref import WeakSet
 
@@ -1456,6 +1471,8 @@
     else:
         zipimport._zip_directory_cache.clear()
         zipimport._zip_directory_cache.update(zdc)
+    encodings._cache.clear()
+    encodings._cache.update(codec_cache)
 
     # clear type cache
     sys._clear_type_cache()
@@ -1498,6 +1515,8 @@
     func1 = sys.getallocatedblocks
     func2 = sys.gettotalrefcount
     gc.collect()
+    gc.collect()
+    gc.collect()
     return func1(), func2()
 
 def warm_caches():
diff -r 5fd1f8271e8a Lib/test/test_codecs.py
--- a/Lib/test/test_codecs.py	Wed Aug 13 09:35:21 2014 +0300
+++ b/Lib/test/test_codecs.py	Wed Aug 13 17:20:15 2014 +1000
@@ -2592,17 +2592,11 @@
         unique_id = repr(self) + str(id(self))
         self.codec_name = encodings.normalize_encoding(unique_id).lower()
 
-        # We store the object to raise on the instance because of a bad
-        # interaction between the codec caching (which means we can't
-        # recreate the codec entry) and regrtest refleak hunting (which
-        # runs the same test instance multiple times). This means we
-        # need to ensure the codecs call back in to the instance to find
-        # out which exception to raise rather than binding them in a
-        # closure to an object that may change on the next run
-        self.obj_to_raise = RuntimeError
-
     def tearDown(self):
-        _TEST_CODECS.pop(self.codec_name, None)
+        entry = _TEST_CODECS.pop(self.codec_name, None)
+        if entry is not None:
+            # Forcibly break the cycle
+            entry.encode = entry.decode = None
 
     def set_codec(self, encode, decode):
         codec_info = codecs.CodecInfo(encode, decode,
@@ -2618,13 +2612,10 @@
         self.assertIsInstance(caught.exception.__cause__, exc_type)
         self.assertIsNotNone(caught.exception.__cause__.__traceback__)
 
-    def raise_obj(self, *args, **kwds):
-        # Helper to dynamically change the object raised by a test codec
-        raise self.obj_to_raise
-
     def check_wrapped(self, obj_to_raise, msg, exc_type=RuntimeError):
-        self.obj_to_raise = obj_to_raise
-        self.set_codec(self.raise_obj, self.raise_obj)
+        def raise_obj(self, *args, **kwds):
+            raise obj_to_raise
+        self.set_codec(raise_obj, raise_obj)
         with self.assertWrapped("encoding", exc_type, msg):
             "str_input".encode(self.codec_name)
         with self.assertWrapped("encoding", exc_type, msg):
@@ -2654,6 +2645,7 @@
         self.check_wrapped(MyRuntimeError(msg), msg, MyRuntimeError)
 
     def check_not_wrapped(self, obj_to_raise, msg):
+        # Assumes obj_to_raise is a subclass or instance of RuntimeError
         def raise_obj(*args, **kwds):
             raise obj_to_raise
         self.set_codec(raise_obj, raise_obj)