diff --git a/src/newgrf_config.h b/src/newgrf_config.h
--- a/src/newgrf_config.h
+++ b/src/newgrf_config.h
@@ -153,7 +153,7 @@ struct GRFParameterInfo {
 
 /** Information about GRF, used in the game and (part of it) in savegames */
 struct GRFConfig : ZeroedMemoryAllocator {
-	GRFConfig(const char *filename = nullptr);
+	GRFConfig(const std::string &filename = std::string{});
 	GRFConfig(const GRFConfig &config);
 	~GRFConfig();
 
@@ -162,7 +162,7 @@ struct GRFConfig : ZeroedMemoryAllocator
 
 	GRFIdentifier ident;                        ///< grfid and md5sum to uniquely identify newgrfs
 	uint8 original_md5sum[16];                  ///< MD5 checksum of original file if only a 'compatible' file was loaded
-	char *filename;                             ///< Filename - either with or without full path
+	std::string filename;                       ///< Filename - either with or without full path
 	GRFTextWrapper name;                        ///< NOSAVE: GRF name (Action 0x08)
 	GRFTextWrapper info;                        ///< NOSAVE: GRF info (author, copyright, ...) (Action 0x08)
 	GRFTextWrapper url;                         ///< NOSAVE: URL belonging to this GRF.