diff --git a/ptvp35/__init__.py b/ptvp35/__init__.py
index ba8ec66..c09dddd 100644
--- a/ptvp35/__init__.py
+++ b/ptvp35/__init__.py
@@ -4,7 +4,7 @@ import pathlib
 import pickle
 import shutil
 from io import StringIO
-from typing import Any, Optional, IO, Type
+from typing import Any, Optional, IO, Type, Hashable
 
 
 class Request:
@@ -66,10 +66,21 @@ class KVJson(KVRequest):
     def line(self) -> str:
         return json.dumps({'key': self.key, 'value': self.value}) + "\n"
 
+    @classmethod
+    def _load_key(cls, key: Any) -> Hashable:
+        if isinstance(key, Hashable):
+            return key
+        elif isinstance(key, list):
+            return tuple(map(cls._load_key, key))
+        elif isinstance(key, dict):
+            return tuple((cls._load_key(k), cls._load_key(v)) for k, v in key)
+        else:
+            raise TypeError("unknown KVJson key type, cannot convert to hashable")
+
     @classmethod
     def fromline(cls, line: str) -> 'KVJson':
         d = json.loads(line)
-        return KVJson(d['key'], d['value'], None)
+        return KVJson(cls._load_key(d['key']), d['value'], None)
 
 
 class Db:
@@ -226,8 +237,12 @@ class Db:
             self.__task.cancel()
         await self._dump_buffer()
         self.__file.close()
-        with open(self.__path, "w") as file:
-            self.db2io(self.__mmdb, file)
+        with open(self.__path_backup, "w") as file:
+            self.__initial_size = self.db2io(self.__mmdb, file)
+        self.__path_recover.touch()
+        shutil.copy(self.__path_backup, self.__path)
+        self.__path_recover.unlink()
+        self.__path_backup.unlink()
 
     def _uninitialize(self):
         self.__mmdb = None