diff --git a/src/BufferParams.cpp b/src/BufferParams.cpp
index 916756e147..f8d23ba3af 100644
--- a/src/BufferParams.cpp
+++ b/src/BufferParams.cpp
@@ -907,7 +907,7 @@ bool BufferParams::writeLaTeX(odocstream & os, LaTeXFeatures & features,
 	}
 
 	// handle inputenc etc.
-	os << writeEncodingPreamble(features, texrow);
+	writeEncodingPreamble(os, features, texrow);
 
 	if (!listings_params.empty()) {
 		os << "\\usepackage{listings}\n";
@@ -1369,11 +1369,9 @@ string const BufferParams::babelCall(string const & lang_opts) const
 }
 
 
-docstring const BufferParams::writeEncodingPreamble(LaTeXFeatures & features,
-			      TexRow & texrow) const
+void BufferParams::writeEncodingPreamble(odocstream & os,
+		LaTeXFeatures & features, TexRow & texrow) const
 {
-	odocstringstream os;
-
 	if (inputenc == "auto") {
 		string const doc_encoding =
 			language->encoding()->latexName();
@@ -1429,8 +1427,6 @@ docstring const BufferParams::writeEncodingPreamble(LaTeXFeatures & features,
 		os << "\\usepackage{armtex}\n";
 		texrow.newline();
 	}
-
-	return os.str();
 }
 
 
diff --git a/src/BufferParams.h b/src/BufferParams.h
index 11049c3380..9b9136ff0e 100644
--- a/src/BufferParams.h
+++ b/src/BufferParams.h
@@ -254,7 +254,7 @@ public:
 	/// set up if and how babel is called
 	std::string const babelCall(std::string const & lang_opts) const;
 	/// handle inputenc etc.
-	docstring const writeEncodingPreamble(LaTeXFeatures & features,
+	void writeEncodingPreamble(odocstream & os, LaTeXFeatures & features,
 					      TexRow & texrow) const;
 	/// set up the document fonts
 	std::string const loadFonts(std::string const & rm,
diff --git a/src/graphics/PreviewLoader.cpp b/src/graphics/PreviewLoader.cpp
index a06ca467fa..e87f773d27 100644
--- a/src/graphics/PreviewLoader.cpp
+++ b/src/graphics/PreviewLoader.cpp
@@ -594,7 +594,7 @@ void PreviewLoader::Impl::startLoading()
 	of << "\\batchmode\n";
 	dumpPreamble(of);
 	// handle inputenc etc.
-	of << buffer_.params().writeEncodingPreamble(features, texrow);
+	buffer_.params().writeEncodingPreamble(of, features, texrow);
 	of << "\n\\begin{document}\n";
 	dumpData(of, inprogress.snippets);
 	of << "\n\\end{document}\n";