Pass string as a const reference.
diff --git a/include/json/writer.h b/include/json/writer.h
index 30424b0..7c9ae21 100644
--- a/include/json/writer.h
+++ b/include/json/writer.h
@@ -300,7 +300,7 @@
   /**
    * \param indentation Each level will be indented by this amount extra.
    */
-  StyledStreamWriter(JSONCPP_STRING indentation = "\t");
+  StyledStreamWriter(const JSONCPP_STRING& indentation = "\t");
   ~StyledStreamWriter() {}
 
 public: