diff --git a/diskimage_builder/elements/growvols/static/usr/local/sbin/growvols b/diskimage_builder/elements/growvols/static/usr/local/sbin/growvols
index 0e5d4686..0c3fdc0b 100755
--- a/diskimage_builder/elements/growvols/static/usr/local/sbin/growvols
+++ b/diskimage_builder/elements/growvols/static/usr/local/sbin/growvols
@@ -512,9 +512,11 @@ def main(argv):
     thin_pool = find_thin_pool(devices, group)
     if thin_pool:
         # total size available, reduced by POOL_METADATA_SIZE
-        # rounded down to whole extent
+        # rounded down to whole extent and reduced by 1 extent
+        # for metadata overhead
         size_bytes -= POOL_METADATA_SIZE
         size_bytes -= size_bytes % PHYSICAL_EXTENT_BYTES
+        size_bytes -= PHYSICAL_EXTENT_BYTES
     dev_path = '/dev/%s' % devname
     grow_vols = find_grow_vols(opts, devices, group, size_bytes)
 
diff --git a/diskimage_builder/elements/growvols/tests/test_growvols.py b/diskimage_builder/elements/growvols/tests/test_growvols.py
index db1f87c7..b1622d64 100644
--- a/diskimage_builder/elements/growvols/tests/test_growvols.py
+++ b/diskimage_builder/elements/growvols/tests/test_growvols.py
@@ -601,13 +601,13 @@ class TestGrowvols(base.BaseTestCase):
             mock.call(['vgextend', 'vg', '/dev/sda5']),
             mock.call(['lvextend', '--poolmetadatasize', '+1073741824B',
                        '/dev/mapper/vg-lv_thinpool', '/dev/sda5']),
-            mock.call(['lvextend', '-L+208331079680B',
+            mock.call(['lvextend', '-L+208326885376B',
                        '/dev/mapper/vg-lv_thinpool', '/dev/sda5']),
-            mock.call(['lvextend', '--size', '+41666215936B',
+            mock.call(['lvextend', '--size', '+41662021632B',
                        '/dev/mapper/vg-lv_home']),
-            mock.call(['lvextend', '--size', '+83332431872B',
+            mock.call(['lvextend', '--size', '+83328237568B',
                        '/dev/mapper/vg-lv_var']),
-            mock.call(['lvextend', '--size', '+83332431872B',
+            mock.call(['lvextend', '--size', '+83336626176B',
                        '/dev/mapper/vg-lv_root']),
             mock.call(['xfs_growfs', '/dev/mapper/vg-lv_home']),
             mock.call(['xfs_growfs', '/dev/mapper/vg-lv_var']),