diff --git a/python/message.c b/python/message.c
index b0df69857e..d6c55deedf 100644
--- a/python/message.c
+++ b/python/message.c
@@ -847,9 +847,12 @@ __attribute__((flatten)) static PyObject* PyUpb_CMessage_GetAttr(
   PyObject* ret = PyObject_GenericGetAttr(_self, attr);
   if (ret) return ret;
 
-  // If the attribute wasn't found, look for attributes on the class. But if a
-  // different kind of error (other than AttributeError) was found, return that.
-  if (PyErr_ExceptionMatches(PyExc_AttributeError)) {
+  // Swallow AttributeError if it occurred and try again on the metaclass
+  // to pick up class attributes.  But we have to special-case "Extensions"
+  // which affirmatively returns AttributeError when a message is not
+  // extendable.
+  if (PyErr_ExceptionMatches(PyExc_AttributeError) &&
+      strcmp(PyUpb_GetStrData(attr), "Extensions") != 0) {
     PyErr_Clear();
     return PyUpb_MessageMeta_GetAttr((PyObject*)Py_TYPE(_self), attr);
   }
@@ -986,11 +989,13 @@ PyObject* PyUpb_CMessage_MergeFromString(PyObject* _self, PyObject* arg) {
   const upb_extreg* extreg = upb_symtab_extreg(upb_filedef_symtab(file));
   const upb_msglayout* layout = upb_msgdef_layout(msgdef);
   upb_arena* arena = PyUpb_Arena_Get(self->arena);
+  PyUpb_ModuleState* state = PyUpb_ModuleState_Get();
+  int options =
+      UPB_DECODE_MAXDEPTH(state->allow_oversize_protos ? UINT32_MAX : 100);
   upb_DecodeStatus status =
-      _upb_decode(buf, size, self->ptr.msg, layout, extreg, 0, arena);
+      _upb_decode(buf, size, self->ptr.msg, layout, extreg, options, arena);
   Py_XDECREF(bytes);
   if (status != kUpb_DecodeStatus_Ok) {
-    PyUpb_ModuleState* state = PyUpb_ModuleState_Get();
     PyErr_Format(state->decode_error_class, "Error parsing message");
     return NULL;
   }
@@ -1180,9 +1185,10 @@ PyObject* PyUpb_CMessage_SerializeInternal(PyObject* _self, PyObject* args,
   const upb_msgdef* msgdef = _PyUpb_CMessage_GetMsgdef(self);
   const upb_msglayout* layout = upb_msgdef_layout(msgdef);
   size_t size = 0;
-  int options = 0;
+  int options = UPB_ENCODE_MAXDEPTH(UINT32_MAX);
   if (check_required) options |= UPB_ENCODE_CHECKREQUIRED;
   if (deterministic) options |= UPB_ENCODE_DETERMINISTIC;
+  // Python does not currently have any effective limit on serialization depth.
   char* pb = upb_encode_ex(self->ptr.msg, layout, options, arena, &size);
   PyObject* ret = NULL;
 
@@ -1248,10 +1254,6 @@ static PyObject* PyUpb_CMessage_GetExtensionDict(PyObject* _self,
 
 static PyGetSetDef PyUpb_CMessage_Getters[] = {
     {"Extensions", PyUpb_CMessage_GetExtensionDict, NULL, "Extension dict"},
-    /*
-    {"_extensions_by_name", (getter)GetExtensionsByName, NULL},
-    {"_extensions_by_number", (getter)GetExtensionsByNumber, NULL},
-    */
     {NULL}};
 
 static PyMethodDef PyUpb_CMessage_Methods[] = {
diff --git a/python/minimal_test.py b/python/minimal_test.py
index 26d6553c84..01eef6edc1 100644
--- a/python/minimal_test.py
+++ b/python/minimal_test.py
@@ -32,6 +32,9 @@ from google.protobuf.pyext import _message
 from google.protobuf.internal import api_implementation
 from google.protobuf import unittest_pb2
 from google.protobuf import descriptor_pool
+from google.protobuf import text_format
+from google.protobuf import message_factory
+from google.protobuf import message
 from google.protobuf.internal import factory_test1_pb2
 from google.protobuf.internal import factory_test2_pb2
 from google.protobuf import descriptor_pb2
@@ -72,9 +75,35 @@ class TestMessageExtension(unittest.TestCase):
         test_slice(11, 3, -2)
         test_slice(11, 3, -3)
         test_slice(10, 25, 4)
+    
+    def testExtensionsErrors(self):
+        msg = unittest_pb2.TestAllTypes()
+        self.assertRaises(AttributeError, getattr, msg, 'Extensions')
 
 #TestMessageExtension.test_descriptor_pool.__unittest_expecting_failure__ = True
 
+class OversizeProtosTest(unittest.TestCase):
+  def setUp(self):
+    msg = unittest_pb2.NestedTestAllTypes()
+    m = msg
+    for i in range(101):
+      m = m.child
+    m.Clear()
+    self.p_serialized = msg.SerializeToString()
+    
+  def testAssertOversizeProto(self):
+    from google.protobuf.pyext._message import SetAllowOversizeProtos
+    SetAllowOversizeProtos(False)
+    q = unittest_pb2.NestedTestAllTypes()
+    with self.assertRaises(message.DecodeError):
+      q.ParseFromString(self.p_serialized)
+      print(q)
+  
+  def testSucceedOversizeProto(self):
+    from google.protobuf.pyext._message import SetAllowOversizeProtos
+    SetAllowOversizeProtos(True)
+    q = unittest_pb2.NestedTestAllTypes()
+    q.ParseFromString(self.p_serialized)
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)
diff --git a/python/pb_unit_tests/message_test_wrapper.py b/python/pb_unit_tests/message_test_wrapper.py
index 993f8e0e3d..d73997b81e 100644
--- a/python/pb_unit_tests/message_test_wrapper.py
+++ b/python/pb_unit_tests/message_test_wrapper.py
@@ -26,28 +26,29 @@
 from google.protobuf.internal import message_test
 import unittest
 
-message_test.MessageTest.testBadUtf8String_proto2.__unittest_expecting_failure__ = True
-message_test.MessageTest.testBadUtf8String_proto3.__unittest_expecting_failure__ = True
+# We don't want to support extending repeated fields with nothing; this behavior
+# is marked for deprecation in the existing library.
 message_test.MessageTest.testExtendFloatWithNothing_proto2.__unittest_expecting_failure__ = True
 message_test.MessageTest.testExtendFloatWithNothing_proto3.__unittest_expecting_failure__ = True
 message_test.MessageTest.testExtendInt32WithNothing_proto2.__unittest_expecting_failure__ = True
 message_test.MessageTest.testExtendInt32WithNothing_proto3.__unittest_expecting_failure__ = True
 message_test.MessageTest.testExtendStringWithNothing_proto2.__unittest_expecting_failure__ = True
 message_test.MessageTest.testExtendStringWithNothing_proto3.__unittest_expecting_failure__ = True
+
+# Our float printing suffers from not having dtoa().
 message_test.MessageTest.testFloatPrinting_proto2.__unittest_expecting_failure__ = True
 message_test.MessageTest.testFloatPrinting_proto3.__unittest_expecting_failure__ = True
 message_test.MessageTest.testHighPrecisionDoublePrinting_proto2.__unittest_expecting_failure__ = True
 message_test.MessageTest.testHighPrecisionDoublePrinting_proto3.__unittest_expecting_failure__ = True
-message_test.MessageTest.testInsertRepeatedCompositeField_proto2.__unittest_expecting_failure__ = True
-message_test.MessageTest.testInsertRepeatedCompositeField_proto3.__unittest_expecting_failure__ = True
-message_test.Proto2Test.testExtensionsErrors.__unittest_expecting_failure__ = True
-message_test.Proto2Test.testPythonicInit.__unittest_expecting_failure__ = True
-message_test.Proto2Test.test_documentation.__unittest_expecting_failure__ = True
+
+# For these tests we are throwing the correct error, only the text of the error
+# message is a mismatch.  For technical reasons around the limited API, matching
+# the existing error message exactly is not feasible.
 message_test.Proto3Test.testCopyFromBadType.__unittest_expecting_failure__ = True
-message_test.Proto3Test.testMapDeterministicSerialization.__unittest_expecting_failure__ = True
 message_test.Proto3Test.testMergeFromBadType.__unittest_expecting_failure__ = True
-message_test.OversizeProtosTest.testAssertOversizeProto.__unittest_expecting_failure__ = True
-message_test.OversizeProtosTest.testSucceedOversizeProto.__unittest_expecting_failure__ = True
+
+message_test.Proto2Test.testPythonicInit.__unittest_expecting_failure__ = True
+message_test.Proto2Test.test_documentation.__unittest_expecting_failure__ = True
 
 if __name__ == '__main__':
   unittest.main(module=message_test, verbosity=2)
diff --git a/python/pb_unit_tests/well_known_types_test_wrapper.py b/python/pb_unit_tests/well_known_types_test_wrapper.py
index 22a35d5534..6ded8d4525 100644
--- a/python/pb_unit_tests/well_known_types_test_wrapper.py
+++ b/python/pb_unit_tests/well_known_types_test_wrapper.py
@@ -26,7 +26,5 @@
 from google.protobuf.internal import well_known_types_test
 import unittest
 
-well_known_types_test.AnyTest.testPackDeterministic.__unittest_expecting_failure__ = True
-
 if __name__ == '__main__':
   unittest.main(module=well_known_types_test, verbosity=2)
diff --git a/python/protobuf.c b/python/protobuf.c
index c57728114c..8eb49a46e4 100644
--- a/python/protobuf.c
+++ b/python/protobuf.c
@@ -40,11 +40,28 @@ static void PyUpb_ModuleDealloc(void *module) {
   PyUpb_WeakMap_Free(s->obj_cache);
 }
 
+PyObject* PyUpb_SetAllowOversizeProtos(PyObject* m, PyObject* arg) {
+  if (!arg || !PyBool_Check(arg)) {
+    PyErr_SetString(PyExc_TypeError,
+                    "Argument to SetAllowOversizeProtos must be boolean");
+    return NULL;
+  }
+  PyUpb_ModuleState* state = PyUpb_ModuleState_Get();
+  state->allow_oversize_protos = PyObject_IsTrue(arg);
+  Py_INCREF(arg);
+  return arg;
+}
+
+static PyMethodDef PyUpb_ModuleMethods[] = {
+    {"SetAllowOversizeProtos", PyUpb_SetAllowOversizeProtos, METH_O,
+     "Enable/disable oversize proto parsing."},
+    {NULL, NULL}};
+
 static struct PyModuleDef module_def = {PyModuleDef_HEAD_INIT,
                                         PYUPB_MODULE_NAME,
                                         "Protobuf Module",
                                         sizeof(PyUpb_ModuleState),
-                                        NULL,  // m_methods
+                                        PyUpb_ModuleMethods,  // m_methods
                                         NULL,  // m_slots
                                         NULL,  // m_traverse
                                         NULL,  // m_clear
@@ -302,6 +319,7 @@ PyMODINIT_FUNC PyInit__message(void) {
 
   PyUpb_ModuleState *state = PyUpb_ModuleState_GetFromModule(m);
 
+  state->allow_oversize_protos = false;
   state->wkt_bases = NULL;
   state->obj_cache = PyUpb_WeakMap_New();
 
diff --git a/python/protobuf.h b/python/protobuf.h
index fa9785a15c..75c8e019a1 100644
--- a/python/protobuf.h
+++ b/python/protobuf.h
@@ -83,6 +83,7 @@ typedef struct {
   PyTypeObject *message_meta_type;
 
   // From protobuf.c
+  bool allow_oversize_protos;
   PyObject *wkt_bases;
   PyTypeObject *arena_type;
   PyUpb_WeakMap *obj_cache;
diff --git a/upb/msg.c b/upb/msg.c
index 3555cd26a3..ee7fe4d2fa 100644
--- a/upb/msg.c
+++ b/upb/msg.c
@@ -252,34 +252,36 @@ static void _upb_mapsorter_getkeys(const void *_a, const void *_b, void *a_key,
   _upb_map_fromkey(b_tabkey, b_key, size);
 }
 
+#define UPB_COMPARE_INTEGERS(a, b) ((a) < (b) ? -1 : ((a) == (b) ? 0 : 1))
+
 static int _upb_mapsorter_cmpi64(const void *_a, const void *_b) {
   int64_t a, b;
   _upb_mapsorter_getkeys(_a, _b, &a, &b, 8);
-  return a - b;
+  return UPB_COMPARE_INTEGERS(a, b);
 }
 
 static int _upb_mapsorter_cmpu64(const void *_a, const void *_b) {
   uint64_t a, b;
   _upb_mapsorter_getkeys(_a, _b, &a, &b, 8);
-  return a - b;
+  return UPB_COMPARE_INTEGERS(a, b);
 }
 
 static int _upb_mapsorter_cmpi32(const void *_a, const void *_b) {
   int32_t a, b;
   _upb_mapsorter_getkeys(_a, _b, &a, &b, 4);
-  return a - b;
+  return UPB_COMPARE_INTEGERS(a, b);
 }
 
 static int _upb_mapsorter_cmpu32(const void *_a, const void *_b) {
   uint32_t a, b;
   _upb_mapsorter_getkeys(_a, _b, &a, &b, 4);
-  return a - b;
+  return UPB_COMPARE_INTEGERS(a, b);
 }
 
 static int _upb_mapsorter_cmpbool(const void *_a, const void *_b) {
   bool a, b;
   _upb_mapsorter_getkeys(_a, _b, &a, &b, 1);
-  return a - b;
+  return UPB_COMPARE_INTEGERS(a, b);
 }
 
 static int _upb_mapsorter_cmpstr(const void *_a, const void *_b) {
@@ -287,10 +289,12 @@ static int _upb_mapsorter_cmpstr(const void *_a, const void *_b) {
   _upb_mapsorter_getkeys(_a, _b, &a, &b, UPB_MAPTYPE_STRING);
   size_t common_size = UPB_MIN(a.size, b.size);
   int cmp = memcmp(a.data, b.data, common_size);
-  if (cmp) return cmp;
-  return a.size - b.size;
+  if (cmp) return -cmp;
+  return UPB_COMPARE_INTEGERS(a.size, b.size);
 }
 
+#undef UPB_COMPARE_INTEGERS
+
 bool _upb_mapsorter_pushmap(_upb_mapsorter *s, upb_descriptortype_t key_type,
                             const upb_map *map, _upb_sortedmap *sorted) {
   int map_size = _upb_map_size(map);
diff --git a/upb/text_encode.c b/upb/text_encode.c
index 12840c0fae..09d0f21f86 100644
--- a/upb/text_encode.c
+++ b/upb/text_encode.c
@@ -152,9 +152,24 @@ static void txtenc_string(txtenc *e, upb_strview str, bool bytes) {
 
 static void txtenc_field(txtenc *e, upb_msgval val, const upb_fielddef *f) {
   txtenc_indent(e);
-  txtenc_printf(e, "%s: ", upb_fielddef_name(f));
+  upb_fieldtype_t type = upb_fielddef_type(f);
+  const char* name = upb_fielddef_name(f);
 
-  switch (upb_fielddef_type(f)) {
+  if (type == UPB_TYPE_MESSAGE) {
+    txtenc_printf(e, "%s {", name);
+    txtenc_endfield(e);
+    e->indent_depth++;
+    txtenc_msg(e, val.msg_val, upb_fielddef_msgsubdef(f));
+    e->indent_depth--;
+    txtenc_indent(e);
+    txtenc_putstr(e, "}");
+    txtenc_endfield(e);
+    return;
+  }
+
+  txtenc_printf(e, "%s: ", name);
+
+  switch (type) {
     case UPB_TYPE_BOOL:
       txtenc_putstr(e, val.bool_val ? "true" : "false");
       break;
@@ -185,15 +200,8 @@ static void txtenc_field(txtenc *e, upb_msgval val, const upb_fielddef *f) {
     case UPB_TYPE_ENUM:
       txtenc_enum(val.int32_val, f, e);
       break;
-    case UPB_TYPE_MESSAGE:
-      txtenc_putstr(e, "{");
-      txtenc_endfield(e);
-      e->indent_depth++;
-      txtenc_msg(e, val.msg_val, upb_fielddef_msgsubdef(f));
-      e->indent_depth--;
-      txtenc_indent(e);
-      txtenc_putstr(e, "}");
-      break;
+    default:
+      UPB_UNREACHABLE();
   }
 
   txtenc_endfield(e);