diff --git a/src/mountinfo.c b/src/mountinfo.c
index 82d042e..686a40d 100644
--- a/src/mountinfo.c
+++ b/src/mountinfo.c
@@ -235,6 +235,7 @@ static struct mountinfo_entry *parse_mountinfo_entry(const char *line)
 	if ((entry->mount_opts = parse_next_string_field()) == NULL)
 		goto fail;
 	entry->optional_fields = &entry->line_buf[0] + total_used++;
+	// NOTE: This ensure s that optional_fields is never NULL.
 	strcpy(entry->optional_fields, "");
 	for (;;) {
 		char *opt_field = parse_next_string_field();