--- grub-2.02/util/grub-mkrescue.c	2019-04-21 08:17:18.880000000 +0200
+++ grub-2.02/util/grub-mkrescue.c	2019-04-21 08:17:52.588000000 +0200
@@ -791,7 +791,7 @@
 
       const char *fat_serial_number = getenv ("GRUB_FAT_SERIAL_NUMBER");
       const char *mformat_args[] =
-	{ "mformat", "-C", "-f", "2880", "-L", "16",
+	{ "mformat", "-k", "-C", "-f", "2880", "-L", "16",
 	  fat_serial_number != NULL ? "-N" : "-C",
 	  fat_serial_number != NULL ? fat_serial_number : "-C",
 	  "-i", efiimgfat, "::", NULL };