diff --git a/external/3rd/library/platform/utils/Base/MD5.cpp b/external/3rd/library/platform/utils/Base/MD5.cpp
index 729266dc..8b33aa9c 100644
--- a/external/3rd/library/platform/utils/Base/MD5.cpp
+++ b/external/3rd/library/platform/utils/Base/MD5.cpp
@@ -250,7 +250,7 @@ namespace Base
         }
     }
 
-    void MD5::Update(const string s)
+    void MD5::Update(const string &s)
     {
         vector<char> achar(s.size(),0);
         for (int i=0; i<(int)s.size(); i++)
diff --git a/external/3rd/library/platform/utils/Base/MD5.h b/external/3rd/library/platform/utils/Base/MD5.h
index 78f53b2b..f75745e3 100644
--- a/external/3rd/library/platform/utils/Base/MD5.h
+++ b/external/3rd/library/platform/utils/Base/MD5.h
@@ -37,7 +37,7 @@ namespace Base
             std::vector<char> Final();
             void Update(char char0);
             void Update(State & state1, const std::vector<char> &achar0, int i, int j);
-            void Update(const std::string s);
+            void Update(const std::string &s);
             void Update(const std::vector<char> &achar0);
             void Update(const std::vector<char> &achar0, int i);
             void Update(const std::vector<char> &achar0, int i, int j);