diff --git a/python/BUILD b/python/BUILD
index 5db0894d31..3bb4a1e2b8 100644
--- a/python/BUILD
+++ b/python/BUILD
@@ -203,6 +203,7 @@ py_extension(
         "-Wno-pedantic",
     ],
     deps = [
+        "//:collections",
         "//:descriptor_upb_proto_reflection",
         "//:reflection",
         "//:table",
diff --git a/python/map.c b/python/map.c
index 35d3d325b2..482e62fb64 100644
--- a/python/map.c
+++ b/python/map.c
@@ -30,6 +30,7 @@
 #include "python/convert.h"
 #include "python/message.h"
 #include "python/protobuf.h"
+#include "upb/collections.h"
 
 // -----------------------------------------------------------------------------
 // MapContainer
@@ -145,6 +146,21 @@ upb_Map* PyUpb_MapContainer_EnsureReified(PyObject* _self) {
   return map;
 }
 
+bool PyUpb_MapContainer_Set(PyUpb_MapContainer* self, upb_Map* map,
+                            upb_MessageValue key, upb_MessageValue val,
+                            upb_Arena* arena) {
+  switch (upb_Map_Insert(map, key, val, arena)) {
+    case kUpb_MapInsertStatus_Inserted:
+      return true;
+    case kUpb_MapInsertStatus_Replaced:
+      // We did not insert a new key, undo the previous invalidate.
+      self->version--;
+      return true;
+    case kUpb_MapInsertStatus_OutOfMemory:
+      return false;
+  }
+}
+
 int PyUpb_MapContainer_AssignSubscript(PyObject* _self, PyObject* key,
                                        PyObject* val) {
   PyUpb_MapContainer* self = (PyUpb_MapContainer*)_self;
@@ -159,7 +175,7 @@ int PyUpb_MapContainer_AssignSubscript(PyObject* _self, PyObject* key,
 
   if (val) {
     if (!PyUpb_PyToUpb(val, val_f, &u_val, arena)) return -1;
-    upb_Map_Set(map, u_key, u_val, arena);
+    if (!PyUpb_MapContainer_Set(self, map, u_key, u_val, arena)) return -1;
   } else {
     if (!upb_Map_Delete(map, u_key)) {
       PyErr_Format(PyExc_KeyError, "Key not present in map");
@@ -187,7 +203,7 @@ PyObject* PyUpb_MapContainer_Subscript(PyObject* _self, PyObject* key) {
     } else {
       memset(&u_val, 0, sizeof(u_val));
     }
-    upb_Map_Set(map, u_key, u_val, arena);
+    if (!PyUpb_MapContainer_Set(self, map, u_key, u_val, arena)) return false;
   }
   return PyUpb_UpbToPy(u_val, val_f, self->arena);
 }
diff --git a/python/pb_unit_tests/message_test_wrapper.py b/python/pb_unit_tests/message_test_wrapper.py
index 040ffded0b..bb1b6c7de9 100644
--- a/python/pb_unit_tests/message_test_wrapper.py
+++ b/python/pb_unit_tests/message_test_wrapper.py
@@ -47,7 +47,6 @@ Proto3Test.testCopyFromBadType.__unittest_expecting_failure__ = True
 Proto3Test.testMergeFromBadType.__unittest_expecting_failure__ = True
 
 Proto2Test.test_documentation.__unittest_expecting_failure__ = True
-Proto3Test.testModifyMapEntryWhileIterating.__unittest_expecting_failure__ = True
 
 if __name__ == '__main__':
   unittest.main(verbosity=2)
diff --git a/upb/collections.c b/upb/collections.c
index a0de0407a5..6bf7fbbbc0 100644
--- a/upb/collections.c
+++ b/upb/collections.c
@@ -147,9 +147,10 @@ bool upb_Map_Get(const upb_Map* map, upb_MessageValue key,
 
 void upb_Map_Clear(upb_Map* map) { _upb_Map_Clear(map); }
 
-bool upb_Map_Set(upb_Map* map, upb_MessageValue key, upb_MessageValue val,
-                 upb_Arena* arena) {
-  return _upb_Map_Set(map, &key, map->key_size, &val, map->val_size, arena);
+upb_MapInsertStatus upb_Map_Insert(upb_Map* map, upb_MessageValue key,
+                                   upb_MessageValue val, upb_Arena* arena) {
+  return (upb_MapInsertStatus)_upb_Map_Insert(map, &key, map->key_size, &val,
+                                              map->val_size, arena);
 }
 
 bool upb_Map_Delete(upb_Map* map, upb_MessageValue key) {
diff --git a/upb/collections.h b/upb/collections.h
index fa28d83cf7..047e14ef68 100644
--- a/upb/collections.h
+++ b/upb/collections.h
@@ -110,10 +110,28 @@ bool upb_Map_Get(const upb_Map* map, upb_MessageValue key,
 /* Removes all entries in the map. */
 void upb_Map_Clear(upb_Map* map);
 
-/* Sets the given key to the given value.  Returns true if this was a new key in
- * the map, or false if an existing key was replaced. */
-bool upb_Map_Set(upb_Map* map, upb_MessageValue key, upb_MessageValue val,
-                 upb_Arena* arena);
+typedef enum {
+  // LINT.IfChange
+  kUpb_MapInsertStatus_Inserted = 0,
+  kUpb_MapInsertStatus_Replaced = 1,
+  kUpb_MapInsertStatus_OutOfMemory = 2,
+  // LINT.ThenChange(//depot/google3/third_party/upb/upb/msg_internal.h)
+} upb_MapInsertStatus;
+
+/* Sets the given key to the given value, returning whether the key was inserted
+ * or replaced.  If the key was inserted, then any existing iterators will be
+ * invalidated. */
+upb_MapInsertStatus upb_Map_Insert(upb_Map* map, upb_MessageValue key,
+                                   upb_MessageValue val, upb_Arena* arena);
+
+/* Sets the given key to the given value.  Returns false if memory allocation
+ * failed. If the key is newly inserted, then any existing iterators will be
+ * invalidated. */
+UPB_INLINE bool upb_Map_Set(upb_Map* map, upb_MessageValue key,
+                            upb_MessageValue val, upb_Arena* arena) {
+  return upb_Map_Insert(map, key, val, arena) !=
+         kUpb_MapInsertStatus_OutOfMemory;
+}
 
 /* Deletes this key from the table.  Returns true if the key was present. */
 bool upb_Map_Delete(upb_Map* map, upb_MessageValue key);
diff --git a/upb/decode.c b/upb/decode.c
index 0985abc965..e6dac273c3 100644
--- a/upb/decode.c
+++ b/upb/decode.c
@@ -653,7 +653,10 @@ static const char* decode_tomap(upb_Decoder* d, const char* ptr,
       decode_err(d, kUpb_DecodeStatus_OutOfMemory);
     }
   } else {
-    _upb_Map_Set(map, &ent.k, map->key_size, &ent.v, map->val_size, &d->arena);
+    if (_upb_Map_Insert(map, &ent.k, map->key_size, &ent.v, map->val_size,
+                        &d->arena) == _kUpb_MapInsertStatus_OutOfMemory) {
+      decode_err(d, kUpb_DecodeStatus_OutOfMemory);
+    }
   }
   return ptr;
 }
diff --git a/upb/msg_internal.h b/upb/msg_internal.h
index b5d8b5c7dd..584ed775fb 100644
--- a/upb/msg_internal.h
+++ b/upb/msg_internal.h
@@ -667,15 +667,31 @@ UPB_INLINE void* _upb_map_next(const upb_Map* map, size_t* iter) {
   return (void*)str_tabent(&it);
 }
 
-UPB_INLINE bool _upb_Map_Set(upb_Map* map, const void* key, size_t key_size,
-                             void* val, size_t val_size, upb_Arena* a) {
+typedef enum {
+  // LINT.IfChange
+  _kUpb_MapInsertStatus_Inserted = 0,
+  _kUpb_MapInsertStatus_Replaced = 1,
+  _kUpb_MapInsertStatus_OutOfMemory = 2,
+  // LINT.ThenChange(//depot/google3/third_party/upb/upb/collections.h)
+} _upb_MapInsertStatus;
+
+UPB_INLINE _upb_MapInsertStatus _upb_Map_Insert(upb_Map* map, const void* key,
+                                                size_t key_size, void* val,
+                                                size_t val_size, upb_Arena* a) {
   upb_StringView strkey = _upb_map_tokey(key, key_size);
   upb_value tabval = {0};
-  if (!_upb_map_tovalue(val, val_size, &tabval, a)) return false;
+  if (!_upb_map_tovalue(val, val_size, &tabval, a)) {
+    return _kUpb_MapInsertStatus_OutOfMemory;
+  }
 
   /* TODO(haberman): add overwrite operation to minimize number of lookups. */
-  upb_strtable_remove2(&map->table, strkey.data, strkey.size, NULL);
-  return upb_strtable_insert(&map->table, strkey.data, strkey.size, tabval, a);
+  bool removed =
+      upb_strtable_remove2(&map->table, strkey.data, strkey.size, NULL);
+  if (!upb_strtable_insert(&map->table, strkey.data, strkey.size, tabval, a)) {
+    return _kUpb_MapInsertStatus_OutOfMemory;
+  }
+  return removed ? _kUpb_MapInsertStatus_Replaced
+                 : _kUpb_MapInsertStatus_Inserted;
 }
 
 UPB_INLINE bool _upb_Map_Delete(upb_Map* map, const void* key,
@@ -717,7 +733,8 @@ UPB_INLINE bool _upb_msg_map_set(upb_Message* msg, size_t ofs, const void* key,
   if (!*map) {
     *map = _upb_Map_New(arena, key_size, val_size);
   }
-  return _upb_Map_Set(*map, key, key_size, val, val_size, arena);
+  return _upb_Map_Insert(*map, key, key_size, val, val_size, arena) !=
+         _kUpb_MapInsertStatus_OutOfMemory;
 }
 
 UPB_INLINE bool _upb_msg_map_delete(upb_Message* msg, size_t ofs,