diff --git a/indra/llfilesystem/lldiskcache.cpp b/indra/llfilesystem/lldiskcache.cpp
index da3530604d..f2ecd9f5b0 100644
--- a/indra/llfilesystem/lldiskcache.cpp
+++ b/indra/llfilesystem/lldiskcache.cpp
@@ -534,7 +534,7 @@ void LLDiskCache::removeOldVFSFiles()
     }
 }
 
-uintmax_t LLDiskCache::dirFileSize(const std::string dir)
+uintmax_t LLDiskCache::dirFileSize(const std::string& dir)
 {
     uintmax_t total_file_size = 0;
 
diff --git a/indra/llfilesystem/lldiskcache.h b/indra/llfilesystem/lldiskcache.h
index f3b5c36e3f..4b51b66e1f 100644
--- a/indra/llfilesystem/lldiskcache.h
+++ b/indra/llfilesystem/lldiskcache.h
@@ -164,7 +164,7 @@ class LLDiskCache :
          * directory. Primarily used here to determine the directory size
          * before and after the cache purge
          */
-        uintmax_t dirFileSize(const std::string dir);
+        uintmax_t dirFileSize(const std::string& dir);
 
         /**
          * Utility function to convert an LLAssetType enum into a