diff --git a/subiquity/controllers/filesystem.py b/subiquity/controllers/filesystem.py
index 8b26dba6..b4a8f093 100644
--- a/subiquity/controllers/filesystem.py
+++ b/subiquity/controllers/filesystem.py
@@ -16,7 +16,6 @@
 import logging
 from subiquity.controller import ControllerPolicy
 from subiquity.models import FilesystemModel
-from subiquity.models.blockdev import FIRST_PARTITION_OFFSET
 from subiquity.ui.views import (DiskPartitionView, AddPartitionView,
                                 FilesystemView)
 from subiquity.ui.dummy import DummyView
@@ -97,14 +96,18 @@ class FilesystemController(ControllerPolicy):
             if current_disk.parttype == 'gpt' and \
                len(current_disk.disk.partitions) == 0:
                 log.debug('Adding grub_bios gpt partition first')
-                current_disk.add_partition(partnum=1,
-                                           size=BIOS_GRUB_SIZE_BYTES,
-                                           fstype=None,
-                                           flag='bios_grub')
+                size_added = \
+                    current_disk.add_partition(partnum=1,
+                                               size=BIOS_GRUB_SIZE_BYTES,
+                                               fstype=None,
+                                               flag='bios_grub')
 
                 # adjust downward the partition size to accommodate
                 # the offset and bios/grub partition
-                spec['bytes'] -= FIRST_PARTITION_OFFSET + BIOS_GRUB_SIZE_BYTES
+                log.debug("Adjusting request down:" +
+                          "{} - {} = {}".format(spec['bytes'], size_added,
+                                                spec['bytes'] - size_added))
+                spec['bytes'] -= size_added
                 spec['partnum'] = 2
 
             if spec["fstype"] in ["swap"]:
diff --git a/subiquity/models/blockdev.py b/subiquity/models/blockdev.py
index 4fc14e29..fad466e0 100644
--- a/subiquity/models/blockdev.py
+++ b/subiquity/models/blockdev.py
@@ -29,6 +29,7 @@ from .actions import (
 
 log = logging.getLogger("subiquity.filesystem.blockdev")
 FIRST_PARTITION_OFFSET = 1 << 20  # 1K offset/aligned
+GPT_END_RESERVE = 1 << 20  # save room at the end for GPT
 
 
 # TODO: Bcachepart class
@@ -215,12 +216,23 @@ class Blockdev():
         if fstype in ["swap"]:
             fstype = "linux-swap(v1)"
 
+        # round up length by 1M
+        def _align_up(size, block_size=1 << 30):
+            return size + (block_size - (size % block_size))
+
         if len(self.disk.partitions) == 0:
             offset = FIRST_PARTITION_OFFSET
         else:
             offset = 0
 
-        log.debug('requested start: {} length: {}'.format(offset, size))
+        log.debug('Aligning start and length on 1M boundaries')
+        new_size = _align_up(size + offset)
+        if new_size > self.freespace - GPT_END_RESERVE:
+            new_size = self.freespace - GPT_END_RESERVE
+        log.debug('Old size: {} New size: {}'.format(size, new_size))
+
+        log.debug('requested start: {} length: {}'.format(offset,
+                                                          new_size - offset))
         valid_flags = [
             "boot",
             "lvm",
@@ -232,7 +244,8 @@ class Blockdev():
 
         # create partition and add
         part_action = PartitionAction(self.baseaction, partnum,
-                                      offset, size, flag)
+                                      offset, new_size - offset, flag)
+
         log.debug('PartitionAction:\n{}'.format(part_action.get()))
 
         self.disk.partitions.update({partnum: part_action})
@@ -250,6 +263,7 @@ class Blockdev():
             self._mounts[partpath] = mountpoint
 
         log.debug('Partition Added')
+        return new_size
 
     def is_mounted(self):
         with open('/proc/mounts') as pm: