diff --git a/src/localisation/localisation.c b/src/localisation/localisation.c
index d383892707..7472bd6575 100644
--- a/src/localisation/localisation.c
+++ b/src/localisation/localisation.c
@@ -1296,8 +1296,8 @@ void format_string_raw(utf8 *dest, size_t size, utf8 *src, void *args)
  */
 void format_string_to_upper(utf8 *dest, size_t size, rct_string_id format, void *args)
 {
-	utf8 *end;
-	size_t left;
+	utf8 *end = dest;
+	size_t left = size;
 	format_string_part(&end, &left, format, args);
 	if (left == 0)
 		log_warning("Truncating formatted string \"%s\" to %d bytes.", dest, size);