diff --git a/src/rime/dict/level_db.cc b/src/rime/dict/level_db.cc
index 31e41b7df..21c106611 100644
--- a/src/rime/dict/level_db.cc
+++ b/src/rime/dict/level_db.cc
@@ -345,10 +345,14 @@ bool LevelDb::CommitTransaction() {
 }
 
 template <>
-const string UserDbFormat<LevelDb>::extension(".userdb");
+string UserDbComponent<LevelDb>::extension() const {
+  return ".userdb";
+}
 
 template <>
-const string UserDbFormat<LevelDb>::snapshot_extension(".userdb.txt");
+string UserDbComponent<LevelDb>::snapshot_extension() const {
+  return ".userdb.txt";
+}
 
 template <>
 UserDbWrapper<LevelDb>::UserDbWrapper(const string& db_name)
diff --git a/src/rime/dict/user_db.cc b/src/rime/dict/user_db.cc
index 32a8a8691..d97b30457 100644
--- a/src/rime/dict/user_db.cc
+++ b/src/rime/dict/user_db.cc
@@ -53,11 +53,17 @@ bool UserDbValue::Unpack(const string& value) {
   return true;
 }
 
+static const string plain_userdb_extension(".userdb.txt");
+
 template <>
-const string UserDbFormat<TextDb>::extension(".userdb.txt");
+string UserDbComponent<TextDb>::extension() const {
+  return plain_userdb_extension;
+}
 
 template <>
-const string UserDbFormat<TextDb>::snapshot_extension(".userdb.txt");
+string UserDbComponent<TextDb>::snapshot_extension() const {
+  return plain_userdb_extension;
+}
 
 // key ::= code <space> <Tab> phrase
 
@@ -110,8 +116,7 @@ bool UserDbHelper::UpdateUserInfo() {
 }
 
 bool UserDbHelper::IsUniformFormat(const string& file_name) {
-  return boost::ends_with(file_name,
-                          UserDbFormat<TextDb>::snapshot_extension);
+  return boost::ends_with(file_name, plain_userdb_extension);
 }
 
 bool UserDbHelper::UniformBackup(const string& snapshot_file) {
diff --git a/src/rime/dict/user_db.h b/src/rime/dict/user_db.h
index 168f6af96..a3e1047fd 100644
--- a/src/rime/dict/user_db.h
+++ b/src/rime/dict/user_db.h
@@ -99,27 +99,16 @@ class UserDbWrapper : public BaseDb {
   }
 };
 
-/// Provides information of the db file format by its base class.
-template <class BaseDb>
-struct UserDbFormat {
-  static const string extension;
-  static const string snapshot_extension;
-};
-
 /// Implements a component that serves as a factory for a user db class.
 template <class BaseDb>
 class UserDbComponent : public UserDb::Component {
  public:
-  virtual Db* Create(const string& name) {
+  Db* Create(const string& name) override {
     return new UserDbWrapper<BaseDb>(name + extension());
   }
 
-  virtual string extension() const {
-    return UserDbFormat<BaseDb>::extension;
-  }
-  virtual string snapshot_extension() const {
-    return UserDbFormat<BaseDb>::snapshot_extension;
-  }
+  string extension() const override;
+  string snapshot_extension() const override;
 };
 
 class UserDbMerger : public Sink {
diff --git a/src/rime/lever/user_dict_manager.cc b/src/rime/lever/user_dict_manager.cc
index 515521f24..2a23f049d 100644
--- a/src/rime/lever/user_dict_manager.cc
+++ b/src/rime/lever/user_dict_manager.cc
@@ -67,8 +67,7 @@ bool UserDictManager::Backup(const string& dict_name) {
       return false;
     }
   }
-  string snapshot_file =
-      dict_name + UserDbFormat<TextDb>::snapshot_extension;
+  string snapshot_file = dict_name + user_db_component_->snapshot_extension();
   return db->Backup((dir / snapshot_file).string());
 }
 
@@ -178,8 +177,7 @@ bool UserDictManager::UpgradeUserDict(const string& dict_name) {
       return false;
     }
   }
-  string snapshot_file =
-      dict_name + UserDbFormat<TextDb>::snapshot_extension;
+  string snapshot_file = dict_name + user_db_component_->snapshot_extension();
   fs::path snapshot_path = trash / snapshot_file;
   return legacy_db->Backup(snapshot_path.string()) &&
          legacy_db->Close() &&
@@ -199,8 +197,7 @@ bool UserDictManager::Synchronize(const string& dict_name) {
     }
   }
   // *.userdb.txt
-  string snapshot_file =
-      dict_name + UserDbFormat<TextDb>::snapshot_extension;
+  string snapshot_file = dict_name + user_db_component_->snapshot_extension();
   for (fs::directory_iterator it(sync_dir), end; it != end; ++it) {
     if (!fs::is_directory(it->path()))
       continue;