diff --git a/src/insets/InsetIndex.cpp b/src/insets/InsetIndex.cpp
index 67f932ed97..4227252093 100644
--- a/src/insets/InsetIndex.cpp
+++ b/src/insets/InsetIndex.cpp
@@ -292,7 +292,7 @@ void InsetIndex::latex(otexstream & ios, OutputParams const & runparams_in) cons
 
 
 void InsetIndex::processLatexSorting(otexstream & os, OutputParams const & runparams,
-				docstring const latex, docstring const spart) const
+				docstring const & latex, docstring const & spart) const
 {
 	if (contains(latex, '\\') && !contains(latex, '@')) {
 		// Now we need to validate that all characters in
diff --git a/src/insets/InsetIndex.h b/src/insets/InsetIndex.h
index b3fe2713d9..860281b970 100644
--- a/src/insets/InsetIndex.h
+++ b/src/insets/InsetIndex.h
@@ -81,7 +81,7 @@ private:
 	void latex(otexstream &, OutputParams const &) const override;
 	///
 	void processLatexSorting(otexstream &, OutputParams const &,
-				 docstring const, docstring const) const;
+				 docstring const &, docstring const &) const;
 	///
 	bool showInsetDialog(BufferView *) const override;
 	///