diff --git a/subiquity/common/filesystem/boot.py b/subiquity/common/filesystem/boot.py
index a9f29f20..9aa9fbd8 100644
--- a/subiquity/common/filesystem/boot.py
+++ b/subiquity/common/filesystem/boot.py
@@ -239,7 +239,8 @@ def get_boot_device_plan_uefi(device):
                 plans.append(MountBootEfiPlan(part))
             return MultiStepPlan(plans=plans)
 
-    spec = dict(size=sizes.get_efi_size(device), fstype='fat32', mount=None)
+    size = sizes.get_efi_size(device.size)
+    spec = dict(size=size, fstype='fat32', mount=None)
     if device._m._mount_for_path("/boot/efi") is None:
         spec['mount'] = '/boot/efi'
 
diff --git a/subiquity/common/filesystem/sizes.py b/subiquity/common/filesystem/sizes.py
index fec1375e..c494e721 100644
--- a/subiquity/common/filesystem/sizes.py
+++ b/subiquity/common/filesystem/sizes.py
@@ -45,15 +45,15 @@ rootfs_scale = PartitionScaleFactors(
         maximum=-1)
 
 
-def scale_partitions(all_factors, disk_size):
+def scale_partitions(all_factors, available_space):
     """for the list of scale factors, provide list of scaled partition size.
     Assumes at most one scale factor with maximum==-1, and
-    disk_size is at least as big as the sum of all partition minimums.
+    available_space is at least as big as the sum of all partition minimums.
     The scale factor with maximum==-1 is given all remaining disk space."""
     ret = []
     sum_priorities = sum([factor.priority for factor in all_factors])
     for cur in all_factors:
-        scaled = int((disk_size / sum_priorities) * cur.priority)
+        scaled = int((available_space / sum_priorities) * cur.priority)
         if scaled < cur.minimum:
             ret.append(cur.minimum)
         elif scaled > cur.maximum:
@@ -63,15 +63,15 @@ def scale_partitions(all_factors, disk_size):
     if -1 in ret:
         used = sum(filter(lambda x: x != -1, ret))
         idx = ret.index(-1)
-        ret[idx] = disk_size - used
+        ret[idx] = available_space - used
     return ret
 
 
-def get_efi_size(disk):
+def get_efi_size(available_space):
     all_factors = (uefi_scale, bootfs_scale, rootfs_scale)
-    return scale_partitions(all_factors, disk.size)[0]
+    return scale_partitions(all_factors, available_space)[0]
 
 
-def get_bootfs_size(disk):
+def get_bootfs_size(available_space):
     all_factors = (uefi_scale, bootfs_scale, rootfs_scale)
-    return scale_partitions(all_factors, disk.size)[1]
+    return scale_partitions(all_factors, available_space)[1]
diff --git a/subiquity/common/filesystem/tests/test_manipulator.py b/subiquity/common/filesystem/tests/test_manipulator.py
index 108ee3c2..7ca13371 100644
--- a/subiquity/common/filesystem/tests/test_manipulator.py
+++ b/subiquity/common/filesystem/tests/test_manipulator.py
@@ -474,7 +474,7 @@ class TestFilesystemManipulator(unittest.TestCase):
     def boot_size_for_disk(self, disk):
         bl = disk._m.bootloader
         if bl == Bootloader.UEFI:
-            return sizes.get_efi_size(disk)
+            return sizes.get_efi_size(disk.size)
         elif bl == Bootloader.PREP:
             return sizes.PREP_GRUB_SIZE_BYTES
         else:
diff --git a/subiquity/common/filesystem/tests/test_sizes.py b/subiquity/common/filesystem/tests/test_sizes.py
index e908f5fd..191441ca 100644
--- a/subiquity/common/filesystem/tests/test_sizes.py
+++ b/subiquity/common/filesystem/tests/test_sizes.py
@@ -23,9 +23,6 @@ from subiquity.common.filesystem.sizes import (
     scale_partitions,
     uefi_scale,
     )
-from subiquity.common.filesystem.tests.test_manipulator import make_manipulator
-from subiquity.models.filesystem import Bootloader
-from subiquity.models.tests.test_filesystem import make_disk
 
 
 class TestPartitionSizeScaling(unittest.TestCase):
@@ -59,7 +56,6 @@ class TestPartitionSizeScaling(unittest.TestCase):
         self.assertEqual([500, 500], scale_partitions(psf, 2000))
 
     def test_efi(self):
-        manipulator = make_manipulator(Bootloader.UEFI)
         tests = [
             # something large to hit maximums
             (30 << 30, uefi_scale.maximum, bootfs_scale.maximum),
@@ -67,16 +63,14 @@ class TestPartitionSizeScaling(unittest.TestCase):
             (8 << 30, uefi_scale.minimum, bootfs_scale.minimum),
         ]
         for disk_size, uefi, bootfs in tests:
-            disk = make_disk(manipulator.model, preserve=True, size=disk_size)
-            self.assertEqual(uefi, get_efi_size(disk))
-            self.assertEqual(bootfs, get_bootfs_size(disk))
+            self.assertEqual(uefi, get_efi_size(disk_size))
+            self.assertEqual(bootfs, get_bootfs_size(disk_size))
 
         # something in between for scaling
         disk_size = 20 << 30
-        disk = make_disk(manipulator.model, preserve=True, size=disk_size)
-        efi_size = get_efi_size(disk)
+        efi_size = get_efi_size(disk_size)
         self.assertTrue(uefi_scale.maximum > efi_size)
         self.assertTrue(efi_size > uefi_scale.minimum)
-        bootfs_size = get_bootfs_size(disk)
+        bootfs_size = get_bootfs_size(disk_size)
         self.assertTrue(bootfs_scale.maximum > bootfs_size)
         self.assertTrue(bootfs_size > bootfs_scale.minimum)
diff --git a/subiquity/server/controllers/filesystem.py b/subiquity/server/controllers/filesystem.py
index 371fd8ff..53927442 100644
--- a/subiquity/server/controllers/filesystem.py
+++ b/subiquity/server/controllers/filesystem.py
@@ -148,7 +148,7 @@ class FilesystemController(SubiquityController, FilesystemManipulator):
         if DeviceAction.TOGGLE_BOOT in DeviceAction.supported(disk):
             self.add_boot_disk(disk)
         gap = gaps.largest_gap(disk)
-        size = sizes.get_bootfs_size(disk)
+        size = sizes.get_bootfs_size(gap.size)
         gap_boot, gap_rest = gap.split(size)
         spec = dict(size=size, fstype="ext4", mount='/boot')
         self.create_partition(device=disk, gap=gap_boot, spec=spec)