diff --git a/src/settings.cpp b/src/settings.cpp
--- a/src/settings.cpp
+++ b/src/settings.cpp
@@ -1135,14 +1135,11 @@ static void GRFSaveConfig(IniFile &ini, 
 	const GRFConfig *c;
 
 	for (c = list; c != nullptr; c = c->next) {
-		/* Hex grfid (4 bytes in nibbles), "|", hex md5sum (16 bytes in nibbles), "|", file system path. */
-		char key[4 * 2 + 1 + 16 * 2 + 1 + MAX_PATH];
 		char params[512];
 		GRFBuildParamList(params, c, lastof(params));
 
-		char *pos = key + seprintf(key, lastof(key), "%08X|", BSWAP32(c->ident.grfid));
-		pos = md5sumToString(pos, lastof(key), c->ident.md5sum);
-		seprintf(pos, lastof(key), "|%s", c->filename);
+		std::string key = fmt::format("{:08X}|{}|{}", BSWAP32(c->ident.grfid),
+				MD5SumToString(c->ident.md5sum), c->filename);
 		group->GetItem(key, true)->SetValue(params);
 	}
 }