diff --git a/.bazelrc b/.bazelrc
index b890fcd138..a9a31d2421 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -14,7 +14,7 @@ build:asan --copt=-fsanitize=address --linkopt=-fsanitize=address
 # know of an easy way to do that.
 #
 # We also have to disable pymalloc to avoid triggering Valgrind.
-build:valgrind --run_under='valgrind --leak-check=full --track-origins=yes --trace-children=yes --show-possibly-lost=no --errors-for-leak-kinds=definite --error-exitcode=1' --action_env=PYTHONMALLOC=malloc
+build:valgrind --run_under='valgrind --leak-check=full --track-origins=yes --trace-children=yes --show-leak-kinds=all --error-exitcode=1 --num-callers=500 ' --action_env=PYTHONMALLOC=malloc
 
 build:ubsan --copt=-fsanitize=undefined --linkopt=-fsanitize=undefined --action_env=UBSAN_OPTIONS=halt_on_error=1:print_stacktrace=1
 # Workaround for the fact that Bazel links with $CC, not $CXX
diff --git a/bazel/protobuf.patch b/bazel/protobuf.patch
index 04ed074886..4b3e93813c 100644
--- a/bazel/protobuf.patch
+++ b/bazel/protobuf.patch
@@ -71,3 +71,19 @@
    raise RuntimeError(
        'Could not find golden files.  This test must be run from within the '
        'protobuf source package so that it can read test data files from the '
+
+--- python/google/protobuf/internal/testing_refleaks.py
++++ python/google/protobuf/internal/testing_refleaks.py
+@@ -67,6 +67,12 @@ class ReferenceLeakCheckerMixin(object):
+   NB_RUNS = 3
+ 
+   def run(self, result=None):
++    testMethod = getattr(self, self._testMethodName)
++    expecting_failure_method = getattr(testMethod, "__unittest_expecting_failure__", False)
++    expecting_failure_class = getattr(self, "__unittest_expecting_failure__", False)
++    if expecting_failure_class or expecting_failure_method:
++      return
++
+     # python_message.py registers all Message classes to some pickle global
+     # registry, which makes the classes immortal.
+     # We save a copy of this registry, and reset it before we could references.
diff --git a/python/descriptor.c b/python/descriptor.c
index 34fdddba87..704e47429c 100644
--- a/python/descriptor.c
+++ b/python/descriptor.c
@@ -169,7 +169,9 @@ static PyObject* PyUpb_DescriptorBase_CopyToProto(PyObject* _self,
   PyObject* serialized =
       PyUpb_DescriptorBase_GetSerializedProto(_self, func, layout);
   if (!serialized) return NULL;
-  return PyUpb_CMessage_MergeFromString(py_proto, serialized);
+  PyObject* ret = PyUpb_CMessage_MergeFromString(py_proto, serialized);
+  Py_DECREF(serialized);
+  return ret;
 }
 
 static void PyUpb_DescriptorBase_Dealloc(PyUpb_DescriptorBase* base) {
diff --git a/python/descriptor_pool.c b/python/descriptor_pool.c
index 95e14feaaa..1b0d3259fa 100644
--- a/python/descriptor_pool.c
+++ b/python/descriptor_pool.c
@@ -135,7 +135,10 @@ static bool PyUpb_DescriptorPool_TryLoadFileProto(PyUpb_DescriptorPool* self,
     return false;
   }
   if (proto == Py_None) return true;
-  return PyUpb_DescriptorPool_DoAdd((PyObject*)self, proto) != NULL;
+  PyObject* ret = PyUpb_DescriptorPool_DoAdd((PyObject*)self, proto);
+  bool ok = ret != NULL;
+  Py_XDECREF(ret);
+  return ok;
 }
 
 static bool PyUpb_DescriptorPool_TryLoadSymbol(PyUpb_DescriptorPool* self,
@@ -246,13 +249,14 @@ done:
 
 static PyObject* PyUpb_DescriptorPool_DoAdd(PyObject* _self,
                                             PyObject* file_desc) {
-  PyObject* subargs = PyTuple_New(0);
   if (!PyUpb_CMessage_Check(file_desc)) return NULL;
   const upb_MessageDef* m = PyUpb_CMessage_GetMsgdef(file_desc);
   const char* file_proto_name = "google.protobuf.FileDescriptorProto";
   if (strcmp(upb_MessageDef_FullName(m), file_proto_name) != 0) {
     return PyErr_Format(PyExc_TypeError, "Can only add FileDescriptorProto");
   }
+  PyObject* subargs = PyTuple_New(0);
+  if (!subargs) return NULL;
   PyObject* serialized =
       PyUpb_CMessage_SerializeToString(file_desc, subargs, NULL);
   Py_DECREF(subargs);
diff --git a/python/extension_dict.c b/python/extension_dict.c
index 277da0e161..6139519858 100644
--- a/python/extension_dict.c
+++ b/python/extension_dict.c
@@ -184,7 +184,7 @@ static PyObject* PyUpb_ExtensionIterator_New(PyObject* _ext_dict) {
 
 static void PyUpb_ExtensionIterator_Dealloc(void* _self) {
   PyUpb_ExtensionIterator* self = (PyUpb_ExtensionIterator*)_self;
-  Py_DECREF(&self->msg);
+  Py_DECREF(self->msg);
   PyUpb_Dealloc(_self);
 }
 
diff --git a/python/message.c b/python/message.c
index 7ef2f9219b..e2ac314ab9 100644
--- a/python/message.c
+++ b/python/message.c
@@ -55,6 +55,7 @@ typedef struct {
   // For each member, we note the equivalent expression that we could use in the
   // full (non-limited) API.
   newfunc type_new;            // PyTypeObject.tp_new
+  destructor type_dealloc;     // PyTypeObject.tp_dealloc
   getattrofunc type_getattro;  // PyTypeObject.tp_getattro
   setattrofunc type_setattro;  // PyTypeObject.tp_setattro
   size_t type_basicsize;       // sizeof(PyHeapTypeObject)
@@ -69,6 +70,36 @@ typedef struct {
 // A global containing the values for this process.
 PyUpb_CPythonBits cpython_bits;
 
+destructor upb_Pre310_PyType_GetDeallocSlot(PyTypeObject* type_subclass) {
+  // This is a bit desperate.  We need type_dealloc(), but PyType_GetSlot(type,
+  // Py_tp_dealloc) will return subtype_dealloc().  There appears to be no way
+  // whatsoever to fetch type_dealloc() through the limited API until Python
+  // 3.10.
+  //
+  // To work around this so we attempt to find it by looking for the offset of
+  // tp_dealloc in PyTypeObject, then memcpy() it directly.  This should always
+  // work in practice.
+  //
+  // Starting with Python 3.10 on you can call PyType_GetSlot() on non-heap
+  // types.  We will be able to replace all this hack with just:
+  //
+  //   PyType_GetSlot(&PyType_Type, Py_tp_dealloc)
+  //
+  destructor subtype_dealloc = PyType_GetSlot(type_subclass, Py_tp_dealloc);
+  for (size_t i = 0; i < 2000; i += sizeof(uintptr_t)) {
+    destructor maybe_subtype_dealloc;
+    memcpy(&maybe_subtype_dealloc, (char*)type_subclass + i,
+           sizeof(destructor));
+    if (maybe_subtype_dealloc == subtype_dealloc) {
+      destructor type_dealloc;
+      memcpy(&type_dealloc, (char*)&PyType_Type + i, sizeof(destructor));
+      return type_dealloc;
+    }
+  }
+  assert(false);
+  return NULL;
+}
+
 static bool PyUpb_CPythonBits_Init(PyUpb_CPythonBits* bits) {
   PyObject* bases = NULL;
   PyTypeObject* type = NULL;
@@ -97,6 +128,7 @@ static bool PyUpb_CPythonBits_Init(PyUpb_CPythonBits* bits) {
   if (!type) goto err;
 
   bits->type_new = PyType_GetSlot(type, Py_tp_new);
+  bits->type_dealloc = upb_Pre310_PyType_GetDeallocSlot(type);
   bits->type_getattro = PyType_GetSlot(type, Py_tp_getattro);
   bits->type_setattro = PyType_GetSlot(type, Py_tp_setattro);
 
@@ -105,10 +137,14 @@ static bool PyUpb_CPythonBits_Init(PyUpb_CPythonBits* bits) {
   bits->type_basicsize = PyLong_AsLong(size);
   if (bits->type_basicsize == -1) goto err;
 
-  assert(bits->type_new && bits->type_getattro && bits->type_setattro);
+  assert(bits->type_new);
+  assert(bits->type_dealloc);
+  assert(bits->type_getattro);
+  assert(bits->type_setattro);
 
 #ifndef Py_LIMITED_API
   assert(bits->type_new == PyType_Type.tp_new);
+  assert(bits->type_dealloc == PyType_Type.tp_dealloc);
   assert(bits->type_getattro == PyType_Type.tp_getattro);
   assert(bits->type_setattro == PyType_Type.tp_setattro);
   assert(bits->type_basicsize == sizeof(PyHeapTypeObject));
@@ -249,7 +285,12 @@ static bool PyUpb_CMessage_LookupName(PyUpb_CMessage* self, PyObject* py_name,
   } else if (PyBytes_Check(py_name)) {
     PyBytes_AsStringAndSize(py_name, (char**)&name, &size);
   }
-  if (!name) return NULL;
+  if (!name) {
+    PyErr_Format(exc_type,
+                 "Expected a field name, but got non-string argument %S.",
+                 py_name);
+    return false;
+  }
   const upb_MessageDef* msgdef = _PyUpb_CMessage_GetMsgdef(self);
 
   if (!upb_MessageDef_FindByNameWithSize(msgdef, name, size, f, o)) {
@@ -344,11 +385,18 @@ static bool PyUpb_CMessage_InitMapAttribute(PyObject* _self, PyObject* name,
 static bool PyUpb_CMessage_InitRepeatedAttribute(PyObject* _self,
                                                  PyObject* name,
                                                  PyObject* value) {
+  bool ok = false;
+  PyObject* tmp = NULL;
   PyObject* repeated = PyUpb_CMessage_GetAttr(_self, name);
-  PyObject* tmp = PyUpb_RepeatedContainer_Extend(repeated, value);
-  if (!tmp) return false;
-  Py_DECREF(tmp);
-  return true;
+  if (!repeated) goto err;
+  tmp = PyUpb_RepeatedContainer_Extend(repeated, value);
+  if (!tmp) goto err;
+  ok = true;
+
+err:
+  Py_XDECREF(repeated);
+  Py_XDECREF(tmp);
+  return ok;
 }
 
 static bool PyUpb_CMessage_InitMessageAttribute(PyObject* _self, PyObject* name,
@@ -956,7 +1004,6 @@ static PyObject* PyUpb_CMessage_IsInitialized(PyObject* _self, PyObject* args) {
   if (!PyArg_ParseTuple(args, "|O", &errors)) {
     return NULL;
   }
-  upb_msg* msg = PyUpb_CMessage_GetIfReified(_self);
   if (errors) {
     // We need to collect a list of unset required fields and append it to
     // `errors`.
@@ -964,6 +1011,7 @@ static PyObject* PyUpb_CMessage_IsInitialized(PyObject* _self, PyObject* args) {
   } else {
     // We just need to return a boolean "true" or "false" for whether all
     // required fields are set.
+    upb_msg* msg = PyUpb_CMessage_GetIfReified(_self);
     const upb_MessageDef* m = PyUpb_CMessage_GetMsgdef(_self);
     const upb_DefPool* symtab = upb_FileDef_Pool(upb_MessageDef_File(m));
     bool initialized = !upb_util_HasUnsetRequired(msg, m, symtab, NULL);
@@ -982,7 +1030,7 @@ static PyObject* PyUpb_CMessage_ListFieldsItemKey(PyObject* self,
 static bool PyUpb_CMessage_SortFieldList(PyObject* list) {
   PyUpb_ModuleState* state = PyUpb_ModuleState_Get();
   bool ok = false;
-  PyObject* args = PyList_New(0);
+  PyObject* args = PyTuple_New(0);
   PyObject* kwargs = PyDict_New();
   PyObject* method = PyObject_GetAttrString(list, "sort");
   PyObject* call_result = NULL;
@@ -1262,7 +1310,9 @@ static PyObject* PyUpb_CMessage_FindInitializationErrors(PyObject* _self,
         need = upb_FieldPath_ToText(&fields, buf, size);
         assert(size > need);
       }
-      PyList_Append(ret, PyUnicode_FromString(buf));
+      PyObject* str = PyUnicode_FromString(buf);
+      PyList_Append(ret, str);
+      Py_DECREF(str);
     }
     free(buf);
   }
@@ -1579,9 +1629,10 @@ PyObject* PyUpb_MessageMeta_DoCreateClass(PyObject* py_descriptor,
   assert(!PyUpb_ObjCache_Get(upb_MessageDef_MiniTable(msgdef)));
 
   PyObject* slots = PyTuple_New(0);
-  if (PyDict_SetItemString(dict, "__slots__", slots) < 0) {
-    return NULL;
-  }
+  if (!slots) return NULL;
+  int status = PyDict_SetItemString(dict, "__slots__", slots);
+  Py_DECREF(slots);
+  if (status < 0) return NULL;
 
   // Bases are either:
   //    (CMessage, Message)            # for regular messages
@@ -1607,7 +1658,7 @@ PyObject* PyUpb_MessageMeta_DoCreateClass(PyObject* py_descriptor,
   meta->layout = upb_MessageDef_MiniTable(msgdef);
   Py_INCREF(meta->py_message_descriptor);
 
-  PyUpb_ObjCache_Add(upb_MessageDef_MiniTable(msgdef), ret);
+  PyUpb_ObjCache_Add(meta->layout, ret);
 
   return ret;
 }
@@ -1653,7 +1704,9 @@ static void PyUpb_MessageMeta_Dealloc(PyObject* self) {
   PyUpb_MessageMeta* meta = PyUpb_GetMessageMeta(self);
   PyUpb_ObjCache_Delete(meta->layout);
   Py_DECREF(meta->py_message_descriptor);
-  PyUpb_Dealloc(self);
+  PyTypeObject* tp = Py_TYPE(self);
+  cpython_bits.type_dealloc(self);
+  Py_DECREF(tp);
 }
 
 void PyUpb_MessageMeta_AddFieldNumber(PyObject* self, const upb_FieldDef* f) {
diff --git a/python/pb_unit_tests/descriptor_pool_test_wrapper.py b/python/pb_unit_tests/descriptor_pool_test_wrapper.py
index 3fd5d4e78c..f97001cffa 100644
--- a/python/pb_unit_tests/descriptor_pool_test_wrapper.py
+++ b/python/pb_unit_tests/descriptor_pool_test_wrapper.py
@@ -27,8 +27,6 @@ from google.protobuf.internal import descriptor_pool_test
 import unittest
 import copy
 
-print(unittest)
-
 descriptor_pool_test.AddDescriptorTest.testAddTypeError.__unittest_expecting_failure__ = True
 descriptor_pool_test.AddDescriptorTest.testEnum.__unittest_expecting_failure__ = True
 descriptor_pool_test.AddDescriptorTest.testFile.__unittest_expecting_failure__ = True
diff --git a/python/protobuf.c b/python/protobuf.c
index af0777e0a3..4debeb1342 100644
--- a/python/protobuf.c
+++ b/python/protobuf.c
@@ -335,7 +335,7 @@ PyMODINIT_FUNC PyInit__message(void) {
 
   // Temporary: an cookie we can use in the tests to ensure we are testing upb
   // and not another protobuf library on the system.
-  PyModule_AddObject(m, "_IS_UPB", Py_True);
+  PyModule_AddIntConstant(m, "_IS_UPB", 1);
 
   return m;
 }
diff --git a/python/protobuf.h b/python/protobuf.h
index 312a8773fa..da8ace7baa 100644
--- a/python/protobuf.h
+++ b/python/protobuf.h
@@ -192,11 +192,10 @@ PyObject* PyUpb_Forbidden_New(PyObject* cls, PyObject* args, PyObject* kwds);
 // function can work for any type.
 static inline void PyUpb_Dealloc(void* self) {
   PyTypeObject* tp = Py_TYPE(self);
+  assert(PyType_GetFlags(tp) & Py_TPFLAGS_HEAPTYPE);
   freefunc tp_free = PyType_GetSlot(tp, Py_tp_free);
   tp_free(self);
-  if (PyType_GetFlags(tp) & Py_TPFLAGS_HEAPTYPE) {
-    Py_DECREF(tp);
-  }
+  Py_DECREF(tp);
 }
 
 // Equivalent to the Py_NewRef() function introduced in Python 3.10.  If/when we
diff --git a/python/repeated.c b/python/repeated.c
index 7faa888afb..c40bb1fc95 100644
--- a/python/repeated.c
+++ b/python/repeated.c
@@ -209,10 +209,12 @@ PyObject* PyUpb_RepeatedContainer_DeepCopy(PyObject* _self, PyObject* value) {
   clone->ptr.arr =
       upb_Array_New(PyUpb_Arena_Get(clone->arena), upb_FieldDef_CType(f));
   PyUpb_ObjCache_Add(clone->ptr.arr, (PyObject*)clone);
-  if (!PyUpb_RepeatedContainer_MergeFrom((PyObject*)clone, _self)) {
+  PyObject* result = PyUpb_RepeatedContainer_MergeFrom((PyObject*)clone, _self);
+  if (!result) {
     Py_DECREF(clone);
     return NULL;
-  }
+  } 
+  Py_DECREF(result);
   return (PyObject*)clone;
 }