diff --git a/src/maasserver/models/partition.py b/src/maasserver/models/partition.py
index 62895f83b..832b1db4c 100644
--- a/src/maasserver/models/partition.py
+++ b/src/maasserver/models/partition.py
@@ -248,7 +248,7 @@ class Partition(CleanSave, TimestampedModel):
                     return idx + 1
             elif arch == "ppc64el" and block_device.id == boot_disk.id:
                 return idx + 2
-            elif arch == "amd64" and bios_boot_method != "uefi":
+            elif arch == "amd64" and bios_boot_method != "uefi" and block_device.id == boot_disk.id:
                 if block_device.type == "physical":
                     # Delay the `type` check because it can cause a query. Only
                     # physical block devices get the bios_grub partition.