diff --git a/src/newgrf_config.cpp b/src/newgrf_config.cpp
--- a/src/newgrf_config.cpp
+++ b/src/newgrf_config.cpp
@@ -586,7 +586,7 @@ public:
 	{
 	}
 
-	bool AddFile(const char *filename, size_t basepath_length, const char *tar_filename) override;
+	bool AddFile(const std::string &filename, size_t basepath_length, const std::string &tar_filename) override;
 
 	/** Do the scan for GRFs. */
 	static uint DoScan()
@@ -600,9 +600,9 @@ public:
 	}
 };
 
-bool GRFFileScanner::AddFile(const char *filename, size_t basepath_length, const char *tar_filename)
+bool GRFFileScanner::AddFile(const std::string &filename, size_t basepath_length, const std::string &tar_filename)
 {
-	GRFConfig *c = new GRFConfig(filename + basepath_length);
+	GRFConfig *c = new GRFConfig(filename.c_str() + basepath_length);
 
 	bool added = true;
 	if (FillGRFDetails(c, false)) {