diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -550,7 +550,7 @@ struct NewGRFTextfileWindow : public Tex
 		this->LoadTextfile(textfile, NEWGRF_DIR);
 	}
 
-	/* virtual */ void SetStringParameters(int widget) const
+	void SetStringParameters(int widget) const override
 	{
 		if (widget == WID_TF_CAPTION) {
 			SetDParam(0, STR_CONTENT_TYPE_NEWGRF);