diff --git a/src/braft/raft_meta.cpp b/src/braft/raft_meta.cpp
index 57590188..2ce73a51 100644
--- a/src/braft/raft_meta.cpp
+++ b/src/braft/raft_meta.cpp
@@ -106,7 +106,7 @@ class MetaStorageManager {
     typedef butil::DoublyBufferedData<MetaStorageMap> DoublyBufferedMetaStorageMap;
     
     static size_t _add(MetaStorageMap& m, const std::string& path, 
-                       const scoped_refptr<KVBasedMergedMetaStorageImpl> mss) {
+                       const scoped_refptr<KVBasedMergedMetaStorageImpl>& mss) {
         std::pair<MetaStorageMap::const_iterator, bool> iter = 
                                         m.insert(std::make_pair(path, mss));
         if (iter.second) {
diff --git a/src/braft/raft_meta.h b/src/braft/raft_meta.h
index 8b849904..2d4200a0 100644
--- a/src/braft/raft_meta.h
+++ b/src/braft/raft_meta.h
@@ -143,11 +143,12 @@ friend class scoped_refptr<KVBasedMergedMetaStorageImpl>;
 
 public:
     explicit KVBasedMergedMetaStorageImpl(const std::string& path)
-        : _is_inited(false), _path(path) {}
+        : _is_inited(false), _path(path), _db(nullptr) {}
     KVBasedMergedMetaStorageImpl() {}
     virtual ~KVBasedMergedMetaStorageImpl() {
         if (_db) {
             delete _db;
+            _db = nullptr;
         }
     }