diff --git a/subiquity/controllers/filesystem.py b/subiquity/controllers/filesystem.py
index 8c233df6..92da5b5e 100644
--- a/subiquity/controllers/filesystem.py
+++ b/subiquity/controllers/filesystem.py
@@ -313,15 +313,14 @@ class FilesystemController(BaseController):
                 # must be wiped or grub-install will fail
                 wipe='zero',
                 flag='prep')
+            self.model.grub_install_device = part
         elif bootloader == Bootloader.BIOS:
             log.debug('Adding grub_bios gpt partition first')
             part = self.create_partition(
                 disk,
                 dict(size=BIOS_GRUB_SIZE_BYTES, fstype=None, mount=None),
                 flag='bios_grub')
-        # should _not_ specify grub device for prep
-        if bootloader != Bootloader.PREP:
-            disk.grub_device = True
+            self.model.grub_install_device = disk
         return part
 
     def create_raid(self, spec):
@@ -472,7 +471,6 @@ class FilesystemController(BaseController):
             boot_disk = boot_partition.device
             full = boot_disk.free_for_partitions == 0
             self.delete_partition(boot_partition)
-            boot_disk.grub_device = False
             if full:
                 largest_part = max(
                     boot_disk.partitions(), key=lambda p: p.size)
diff --git a/subiquity/models/filesystem.py b/subiquity/models/filesystem.py
index c4263d65..6d479690 100644
--- a/subiquity/models/filesystem.py
+++ b/subiquity/models/filesystem.py
@@ -555,10 +555,17 @@ class Disk(_Device):
         lambda self: len(self._partitions) == 0 and
         self._constructed_device is None)
     _can_REMOVE = property(_generic_can_REMOVE)
-    _can_MAKE_BOOT = property(
-        lambda self:
-        not self.grub_device and self._fs is None
-        and self._constructed_device is None)
+
+    @property
+    def _can_MAKE_BOOT(self):
+        install_dev = self._m.grub_install_device
+        if install_dev:
+            # For the PReP case, the install_device is the prep partition.
+            if install_dev.type == "partition":
+                install_dev = install_dev.device
+            if install_dev is self:
+                return False
+        return self._fs is None and self._constructed_device is None
 
     ok_for_raid = ok_for_lvm_vg = _can_FORMAT
 
@@ -918,6 +925,7 @@ class FilesystemModel(object):
     def reset(self):
         self._actions = [
             Disk.from_info(self, info) for info in self._disk_info]
+        self.grub_install_device = None
 
     def _render_actions(self):
         # The curtin storage config has the constraint that an action must be
@@ -982,6 +990,15 @@ class FilesystemModel(object):
             }
         if not self._should_add_swapfile():
             config['swap'] = {'size': 0}
+        if self.grub_install_device:
+            dev = self.grub_install_device
+            if dev.type == "partition":
+                devpath = "{}{}".format(dev.device.path, dev._number)
+            else:
+                devpath = dev.path
+            config['grub'] = {
+                'install_devices': [devpath],
+                }
         return config
 
     def _get_system_mounted_disks(self):
diff --git a/subiquity/ui/views/filesystem/tests/test_filesystem.py b/subiquity/ui/views/filesystem/tests/test_filesystem.py
index 4acd1d02..5232acdd 100644
--- a/subiquity/ui/views/filesystem/tests/test_filesystem.py
+++ b/subiquity/ui/views/filesystem/tests/test_filesystem.py
@@ -25,6 +25,7 @@ class FilesystemViewTests(unittest.TestCase):
         controller = mock.create_autospec(spec=FilesystemController)
         controller.ui = mock.Mock()
         model.all_devices.return_value = devices
+        model.grub_install_device = None
         return FilesystemView(model, controller)
 
     def test_simple(self):