diff --git a/mace/core/file_storage.cc b/mace/core/file_storage.cc
index eb48cfed393576141d7c2f6e9fc3ea7f0a51e6e1..d0030d2bd91b470f7bbaaa09a5d3c9ee9fb39ca9 100644
--- a/mace/core/file_storage.cc
+++ b/mace/core/file_storage.cc
@@ -104,7 +104,6 @@ void FileStorage::Load() {
   if (res != 0) {
     LOG(WARNING) << "munmap file " << file_path_
                  << " failed, error code: " << errno;
-    return;
   }
   res = close(fd);
   if (res != 0) {
@@ -119,7 +118,7 @@ bool FileStorage::Insert(const std::string &key,
   return true;
 }
 
-std::vector<unsigned char> *FileStorage::Find(const std::string &key) {
+const std::vector<unsigned char> *FileStorage::Find(const std::string &key) {
   auto iter = data_.find(key);
   if (iter == data_.end()) return nullptr;
 
diff --git a/mace/core/file_storage.h b/mace/core/file_storage.h
index b1c90b50351f559a0d0a8315256b39fa1eeb6bca..7c777e7edd6c32a6694c92f2d538cceadb06d1c6 100644
--- a/mace/core/file_storage.h
+++ b/mace/core/file_storage.h
@@ -21,7 +21,7 @@ class FileStorage : public KVStorage {
   void Load() override;
   bool Insert(const std::string &key,
               const std::vector<unsigned char> &value) override;
-  std::vector<unsigned char> *Find(const std::string &key) override;
+  const std::vector<unsigned char> *Find(const std::string &key) override;
   void Flush() override;
 
  private:
diff --git a/mace/public/mace_runtime.h b/mace/public/mace_runtime.h
index 55397701397647318bfefbbb0b2a3a443c502ae7..46500994642b29e16dadacfa2cac3a1c597c9cb8 100644
--- a/mace/public/mace_runtime.h
+++ b/mace/public/mace_runtime.h
@@ -36,7 +36,7 @@ class KVStorage {
   virtual void Load() = 0;
   virtual bool Insert(const std::string &key,
                       const std::vector<unsigned char> &value) = 0;
-  virtual std::vector<unsigned char> *Find(const std::string &key) = 0;
+  virtual const std::vector<unsigned char> *Find(const std::string &key) = 0;
   virtual void Flush() = 0;
 };