diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index 413e44f28ec955..83fa85d748a055 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -386,6 +386,28 @@ PyAPI_FUNC(PyObject *) _PyObject_FunctionStr(PyObject *);
     } while (0)
 #endif
 
+/* Py_XSETREF_WITH_REGION() is a region-aware variant of Py_XSETREF */
+#ifdef _Py_TYPEOF
+#define Py_XSETREF_WITH_REGION(dst, src, obj) \
+    do { \
+        _Py_TYPEOF(dst)* _tmp_dst_ptr = &(dst); \
+        _Py_TYPEOF(dst) _tmp_old_dst = (*_tmp_dst_ptr); \
+        *_tmp_dst_ptr = (src); \
+        if (_tmp_old_dst) Py_REGIONREMOVEREFERENCE(obj, _tmp_old_dst); \
+        Py_XDECREF(_tmp_old_dst); \
+    } while (0)
+#else
+#define Py_XSETREF_WITH_REGION(dst, src, obj) \
+    do { \
+        PyObject **_tmp_dst_ptr = _Py_CAST(PyObject**, &(dst)); \
+        PyObject *_tmp_old_dst = (*_tmp_dst_ptr); \
+        PyObject *_tmp_src = _PyObject_CAST(src); \
+        memcpy(_tmp_dst_ptr, &_tmp_src, sizeof(PyObject*)); \
+        if (_tmp_old_dst) Py_REGIONREMOVEREFERENCE(obj, _tmp_old_dst); \
+        Py_XDECREF(_tmp_old_dst); \
+    } while (0)
+#endif
+
 
 PyAPI_DATA(PyTypeObject) _PyNone_Type;
 PyAPI_DATA(PyTypeObject) _PyNotImplemented_Type;
diff --git a/Include/internal/pycore_regions.h b/Include/internal/pycore_regions.h
index 6a2c808ec2987a..c4c770046362b5 100644
--- a/Include/internal/pycore_regions.h
+++ b/Include/internal/pycore_regions.h
@@ -12,6 +12,9 @@ extern "C" {
 #include "object.h"
 #include "regions.h"
 
+#define Py_IS_REGION_AWARE(tp) (tp->tp_flags & Py_TPFLAGS_REGION_AWARE)
+#define Py_OBJ_IS_REGION_AWARE(op) Py_IS_REGION_AWARE(Py_TYPE(op))
+
 #define Py_CHECKWRITE(op) ((op) && !Py_IsImmutable(op))
 #define Py_REQUIREWRITE(op, msg) {if (Py_CHECKWRITE(op)) { _PyObject_ASSERT_FAILED_MSG(op, msg); }}
 
@@ -56,7 +59,6 @@ PyObject* _Py_EnableInvariant(void);
 PyObject* _Py_ResetInvariant(void);
 #define Py_ResetInvariant() _Py_ResetInvariant()
 
-// Invariant placeholder
 bool _Py_RegionAddReference(PyObject* src, PyObject* new_tgt);
 #define Py_REGIONADDREFERENCE(a, b) _Py_RegionAddReference(_PyObject_CAST(a), b)
 
@@ -92,6 +94,7 @@ PyObject *_PyCown_close_region(PyObject* ob);
 #define PyCown_close_region(op) _PyCown_close_region(_PyObject_CAST(op))
 int _PyRegion_is_closed(PyObject* op);
 #define PyRegion_is_closed(op) _PyRegion_is_closed(_PyObject_CAST(op))
+void _PyObject_mark_region_as_dirty(PyObject *op);
 
 
 #ifdef _Py_TYPEOF
diff --git a/Objects/cellobject.c b/Objects/cellobject.c
index 0c7b648605e440..044a334f580f0e 100644
--- a/Objects/cellobject.c
+++ b/Objects/cellobject.c
@@ -1,6 +1,7 @@
 /* Cell object implementation */
 
 #include "Python.h"
+#include "object.h"
 #include "pycore_object.h"
 #include "pycore_regions.h"
 
@@ -186,7 +187,7 @@ PyTypeObject PyCell_Type = {
     PyObject_GenericGetAttr,                    /* tp_getattro */
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,    /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_REGION_AWARE,    /* tp_flags */
     cell_new_doc,                               /* tp_doc */
     (traverseproc)cell_traverse,                /* tp_traverse */
     (inquiry)cell_clear,                        /* tp_clear */
diff --git a/Objects/complexobject.c b/Objects/complexobject.c
index aee03ddfb07aec..0fd14ea3fcd760 100644
--- a/Objects/complexobject.c
+++ b/Objects/complexobject.c
@@ -6,6 +6,7 @@
 /* Submitted by Jim Hugunin */
 
 #include "Python.h"
+#include "object.h"
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
 #include "pycore_long.h"          // _PyLong_GetZero()
 #include "pycore_object.h"        // _PyObject_Init()
@@ -1087,7 +1088,7 @@ PyTypeObject PyComplex_Type = {
     PyObject_GenericGetAttr,                    /* tp_getattro */
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,   /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_REGION_AWARE,   /* tp_flags */
     complex_new__doc__,                         /* tp_doc */
     0,                                          /* tp_traverse */
     0,                                          /* tp_clear */
diff --git a/Objects/cown.c b/Objects/cown.c
index 384fdaba33fb57..44745cdf8c8dd4 100644
--- a/Objects/cown.c
+++ b/Objects/cown.c
@@ -320,7 +320,7 @@ PyTypeObject PyCown_Type = {
     0,                                       /* tp_getattro */
     0,                                       /* tp_setattro */
     0,                                       /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_REGION_AWARE, /* tp_flags */
     0,                                       /* tp_doc */
     (traverseproc)PyCown_traverse,           /* tp_traverse */
     (inquiry)PyCown_clear,                   /* tp_clear */
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 5d9b413861478a..a33b5dffc0c4a4 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -3,6 +3,7 @@
 /* XXX The functional organization of this file is terrible */
 
 #include "Python.h"
+#include "object.h"
 #include "pycore_bitutils.h"      // _Py_popcount32()
 #include "pycore_initconfig.h"    // _PyStatus_OK()
 #include "pycore_long.h"          // _Py_SmallInts
@@ -6271,7 +6272,7 @@ PyTypeObject PyLong_Type = {
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
-        Py_TPFLAGS_LONG_SUBCLASS |
+        Py_TPFLAGS_LONG_SUBCLASS | Py_TPFLAGS_REGION_AWARE |
         _Py_TPFLAGS_MATCH_SELF,               /* tp_flags */
     long_doc,                                   /* tp_doc */
     0,                                          /* tp_traverse */
diff --git a/Objects/object.c b/Objects/object.c
index a9813a999fdb62..29805784645b9c 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -31,6 +31,7 @@ extern "C" {
 
 /* Defined in tracemalloc.c */
 extern void _PyMem_DumpTraceback(int fd, const void *ptr);
+extern int _Py_is_bridge_object(PyObject *op);
 
 
 int
@@ -1173,9 +1174,19 @@ PyObject_SetAttr(PyObject *v, PyObject *name, PyObject *value)
 
     PyUnicode_InternInPlace(&name);
     if (tp->tp_setattro != NULL) {
-        if(Py_CHECKWRITE(v)){
+        if (Py_CHECKWRITE(v)) {
+            if (!Py_IS_REGION_AWARE(tp)) {
+                _PyObject_mark_region_as_dirty(v);
+                // If x.f = y and type(x) isn't region aware,
+                // when y is a bridge object, mark its region
+                // as dirty since we probably just violated the
+                // external uniqueness invariant.
+                if (_Py_is_bridge_object(value)) {
+                    _PyObject_mark_region_as_dirty(value);
+                }
+            }
             err = (*tp->tp_setattro)(v, name, value);
-        }else{
+        } else {
             PyErr_WriteToImmutable(v);
             err = -1;
         }
@@ -1190,9 +1201,19 @@ PyObject_SetAttr(PyObject *v, PyObject *name, PyObject *value)
             return -1;
         }
 
-        if(Py_CHECKWRITE(v)){
+        if (Py_CHECKWRITE(v)) {
+            if (!Py_IS_REGION_AWARE(tp)) {
+                _PyObject_mark_region_as_dirty(v);
+                // If x.f = y and type(x) isn't region aware,
+                // when y is a bridge object, mark its region
+                // as dirty since we probably just violated the
+                // external uniqueness invariant.
+                if (_Py_is_bridge_object(value)) {
+                    _PyObject_mark_region_as_dirty(value);
+                }
+            }
             err = (*tp->tp_setattr)(v, (char *)name_str, value);
-        }else{
+        } else {
             PyErr_WriteToImmutable(v);
             err = -1;
         }
@@ -1667,8 +1688,12 @@ PyObject_GenericSetDict(PyObject *obj, PyObject *value, void *context)
                      "not a '%.200s'", Py_TYPE(value)->tp_name);
         return -1;
     }
-    Py_XSETREF(*dictptr, Py_NewRef(value));
-    return 0;
+    if (Py_REGIONADDREFERENCE(obj, value)) {
+        Py_XSETREF_WITH_REGION(*dictptr, Py_NewRef(value), obj);
+        return 0;
+    } else {
+        return -1;
+    }
 }
 
 
@@ -1895,7 +1920,7 @@ PyTypeObject _PyNone_Type = {
     0,                  /*tp_getattro */
     0,                  /*tp_setattro */
     0,                  /*tp_as_buffer */
-    Py_TPFLAGS_DEFAULT, /*tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_REGION_AWARE, /*tp_flags */
     0,                  /*tp_doc */
     0,                  /*tp_traverse */
     0,                  /*tp_clear */
diff --git a/Objects/regions.c b/Objects/regions.c
index ab7e602e211663..26749de346e00c 100644
--- a/Objects/regions.c
+++ b/Objects/regions.c
@@ -159,8 +159,8 @@ static void regionmetadata_mark_as_dirty(Py_region_ptr_t self_ptr) {
     if (!HAS_METADATA(self_ptr)) {
         return;
     }
-
-    REGION_DATA_CAST(self_ptr)->is_dirty = true;
+    regionmetadata *self = REGION_DATA_CAST(self_ptr);
+    self->is_dirty = true;
 }
 # define regionmetadata_mark_as_dirty(data) \
     (regionmetadata_mark_as_dirty(REGION_PTR_CAST(data)))
@@ -240,6 +240,10 @@ static bool regionmetadata_is_open(Py_region_ptr_t self) {
 #define regionmetadata_is_open(self) \
     regionmetadata_is_open(REGION_PTR_CAST(self))
 
+void _PyObject_mark_region_as_dirty(PyObject *op) {
+    regionmetadata_mark_as_dirty(_Py_REGION(op));
+}
+
 static void regionmetadata_inc_osc(Py_region_ptr_t self_ptr)
 {
     if (!HAS_METADATA(self_ptr)) {
@@ -1874,7 +1878,7 @@ PyTypeObject PyRegion_Type = {
     0,                                       /* tp_getattro */
     0,                                       /* tp_setattro */
     0,                                       /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_REGION_AWARE, /* tp_flags */
     "TODO =^.^=",                            /* tp_doc */
     (traverseproc)PyRegion_traverse,         /* tp_traverse */
     (inquiry)PyRegion_clear,                 /* tp_clear */
@@ -1920,6 +1924,14 @@ static const char *get_region_name(PyObject* obj) {
     }
 }
 
+// TODO replace with write barrier code
+bool _Pyrona_RemoveReference(PyObject *src, PyObject *tgt) {
+#ifndef NDEBUG
+        _Py_VPYDBG("Removed %p --> %p (owner: '%s')\n", src, tgt, get_region_name(src));
+#endif
+    return true; // TODO: implement
+}
+
 // x.f = y ==> _Pyrona_AddReference(src=x, tgt=y)
 bool _Py_RegionAddReference(PyObject *src, PyObject *tgt) {
     if (Py_REGION(src) == Py_REGION(tgt)) {
diff --git a/Objects/tupleobject.c b/Objects/tupleobject.c
index e043054197ae05..c5aa35c6f9c9c4 100644
--- a/Objects/tupleobject.c
+++ b/Objects/tupleobject.c
@@ -2,6 +2,7 @@
 /* Tuple object implementation */
 
 #include "Python.h"
+#include "object.h"
 #include "pycore_abstract.h"      // _PyIndex_Check()
 #include "pycore_gc.h"            // _PyObject_GC_IS_TRACKED()
 #include "pycore_initconfig.h"    // _PyStatus_OK()
@@ -879,7 +880,7 @@ PyTypeObject PyTuple_Type = {
     0,                                          /* tp_as_buffer */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
         Py_TPFLAGS_BASETYPE | Py_TPFLAGS_TUPLE_SUBCLASS |
-        _Py_TPFLAGS_MATCH_SELF | Py_TPFLAGS_SEQUENCE,  /* tp_flags */
+        _Py_TPFLAGS_MATCH_SELF | Py_TPFLAGS_SEQUENCE | Py_TPFLAGS_REGION_AWARE,  /* tp_flags */
     tuple_new__doc__,                           /* tp_doc */
     (traverseproc)tupletraverse,                /* tp_traverse */
     0,                                          /* tp_clear */
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 8547f0f2a86277..3e79a0ff1f16d5 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -1,8 +1,10 @@
 /* Type object implementation */
 
 #include "Python.h"
+#include "object.h"
 #include "pycore_call.h"
 #include "pycore_code.h"          // CO_FAST_FREE
+#include "pycore_regions.h"
 #include "pycore_symtable.h"      // _Py_Mangle()
 #include "pycore_dict.h"          // _PyDict_KeysSize()
 #include "pycore_initconfig.h"    // _PyStatus_OK()
@@ -2940,8 +2942,12 @@ subtype_setdict(PyObject *obj, PyObject *value, void *context)
                      "not a '%.200s'", Py_TYPE(value)->tp_name);
         return -1;
     }
-    Py_XSETREF(*dictptr, Py_XNewRef(value));
-    return 0;
+    if (value == NULL || Py_REGIONADDREFERENCE(obj, value)) {
+        Py_XSETREF_WITH_REGION(*dictptr, Py_XNewRef(value), obj);
+        return 0;
+    } else {
+        return -1;
+    }
 }
 
 static PyObject *
@@ -3326,7 +3332,7 @@ type_new_alloc(type_new_ctx *ctx)
     // All heap types need GC, since we can create a reference cycle by storing
     // an instance on one of its parents.
     type->tp_flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HEAPTYPE |
-                      Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC);
+                      Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_REGION_AWARE);
 
     // Initialize essential fields
     type->tp_as_async = &et->as_async;
@@ -5349,6 +5355,7 @@ PyTypeObject PyType_Type = {
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
     Py_TPFLAGS_BASETYPE | Py_TPFLAGS_TYPE_SUBCLASS |
     Py_TPFLAGS_HAVE_VECTORCALL |
+    Py_TPFLAGS_REGION_AWARE |
     Py_TPFLAGS_ITEMS_AT_END,                    /* tp_flags */
     type_doc,                                   /* tp_doc */
     (traverseproc)type_traverse,                /* tp_traverse */
@@ -6559,7 +6566,8 @@ PyTypeObject PyBaseObject_Type = {
     PyObject_GenericGetAttr,                    /* tp_getattro */
     PyObject_GenericSetAttr,                    /* tp_setattro */
     0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,   /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
+    Py_TPFLAGS_REGION_AWARE,   /* tp_flags */
     object_doc,                                 /* tp_doc */
     0,                                          /* tp_traverse */
     0,                                          /* tp_clear */