--- preseed_storage.py	2018-10-18 09:09:24.372519602 -0700
+++ preseed_storage2.py	2018-10-18 09:10:30.112463704 -0700
@@ -22,6 +22,7 @@
 from maasserver.models.partition import Partition
 from maasserver.models.partitiontable import (
     BIOS_GRUB_PARTITION_SIZE,
+    GPT_REQUIRED_SIZE,
     INITIAL_PARTITION_OFFSET,
     PARTITION_TABLE_EXTRA_SPACE,
     PREP_PARTITION_SIZE,
@@ -127,7 +128,10 @@
         """Return True if block device requires the bios_grub partition."""
         arch, _ = self.node.split_arch()
         bios_boot_method = self.node.get_bios_boot_method()
-        return arch == "amd64" and bios_boot_method != "uefi"
+        return (
+            arch == "amd64" and
+            bios_boot_method != "uefi" and
+            block_device.size >= GPT_REQUIRED_SIZE)

     def _add_partition_operations(self):
         """Add all the partition operations.