https://dev.lovelyhq.com/libburnia/libisoburn/commit/1eb51f44dadb8b6c5f87533ca357186cdc1ac625
diff --git a/frontend/grub-mkrescue-sed.sh b/frontend/grub-mkrescue-sed.sh
index b3948c99..dcd9d696 100755
--- a/frontend/grub-mkrescue-sed.sh
+++ b/frontend/grub-mkrescue-sed.sh
@@ -120,6 +120,7 @@ fi
 # "yes" overwrites the MBR partition table area in the EFI boot image by zeros.
 # Some EFI implementations get stuck when seeing in the EFI partition a
 # partition table entry which begins at LBA 0.
+# "extra" not only zeros the partition table but also the MBR signature.
 efi_zero_inner_pt=no
 if test -n "$MKRESCUE_SED_IN_EFI_NO_PT"
 then
@@ -192,24 +193,31 @@ then
   find "$dir"
 fi
 
-if test "$efi_zero_inner_pt" = yes
+if test "$efi_zero_inner_pt" = yes -o "$efi_zero_inner_pt" = extra
 then
   did_dd=0
   if test -e "$dir"/efi.img
   then
+    # Look for 0x55 0xAA in bytes 510 and 511
     magic=$(dd bs=1 skip=510 count=2 if="$dir"/efi.img 2>/dev/null | \
             od -c | head -1 | awk '{print $2 " " $3}')
     if test "$magic" = "U 252"
     then
+      echo "Performing actions for MKRESCUE_SED_IN_EFI_NO_PT=$efi_zero_inner_pt" >&2
       dd if=/dev/zero bs=1 seek=446 count=64 conv=notrunc of="$dir"/efi.img
       did_dd=1
+      if test "$efi_zero_inner_pt" = extra
+      then
+        dd if=/dev/zero bs=1 seek=510 count=2 conv=notrunc of="$dir"/efi.img
+      fi
+      echo >&2
     fi
   fi
   if test "$did_dd" = 0
   then
     echo >&2
     echo "$0 : NOTE : No EFI image found or no MBR signature in it." >&2
-    echo "$0 : NOTE : Will not obey MKRESCUE_SED_IN_EFI_NO_PT=yes" >&2
+    echo "$0 : NOTE : Will not obey MKRESCUE_SED_IN_EFI_NO_PT=$efi_zero_inner_pt" >&2
     echo >&2
   fi
 fi