diff --git a/libmei/addons/att.h b/libmei/addons/att.h
index d17ab4f46c..b2a511457b 100644
--- a/libmei/addons/att.h
+++ b/libmei/addons/att.h
@@ -42,7 +42,7 @@ class Att : public AttConverterBase {
     static data_STAFFREL_basic StaffrelToStaffrelBasic(data_STAFFREL staffrel);
 
     /** Dummy string converter */
-    std::string StrToStr(const std::string str) const;
+    std::string StrToStr(const std::string &str) const;
 
     /** @name Basic converters for writing */
     ///@{