diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index c43d35fb49..7bd3525373 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -970,7 +970,7 @@ namespace DoExport {
 
 	#if ENABLE_THUMBNAIL_GENERATOR
 	template<typename WriteToOutput, typename ThrowIfCanceledCallback>
-	static void export_thumbnails_to_file(ThumbnailsGeneratorCallback &thumbnail_cb, const std::vector<Vec2d> &sizes, WriteToOutput &output, ThrowIfCanceledCallback throw_if_canceled)
+	static void export_thumbnails_to_file(ThumbnailsGeneratorCallback &thumbnail_cb, const std::vector<Vec2d> &sizes, WriteToOutput output, ThrowIfCanceledCallback throw_if_canceled)
 	{
 	    // Write thumbnails using base64 encoding
 	    if (thumbnail_cb != nullptr)