diff --git a/diskimage_builder/elements/growvols/static/usr/local/sbin/growvols b/diskimage_builder/elements/growvols/static/usr/local/sbin/growvols
index 8894bed4..e677d8c8 100755
--- a/diskimage_builder/elements/growvols/static/usr/local/sbin/growvols
+++ b/diskimage_builder/elements/growvols/static/usr/local/sbin/growvols
@@ -475,7 +475,7 @@ def find_thin_pool(devices, group):
             break
 
     if not thin_pool_device:
-        return
+        return None, None
 
     # ensure every volume uses the pool
     for d in lvs_devices:
@@ -490,7 +490,7 @@ def find_thin_pool(devices, group):
             raise Exception('All volumes need to be in pool %s. '
                             '%s is in pool %s' %
                             (thin_pool_name, lv_name, pool_lv))
-    return thin_pool_device
+    return thin_pool_device, thin_pool_name
 
 
 def main(argv):
@@ -522,13 +522,16 @@ def main(argv):
     group = find_group(opts)
     partnum = find_next_partnum(devices, disk_name)
     devname = find_next_device_name(devices, disk_name, partnum)
-    thin_pool = find_thin_pool(devices, group)
+    thin_pool, thin_pool_name = find_thin_pool(devices, group)
     if thin_pool:
-        # total size available, reduced by POOL_METADATA_SIZE
-        # rounded down to whole extent and reduced by 1 extent
-        # for metadata overhead
+        # reserve for the size of the metadata volume
         size_bytes -= POOL_METADATA_SIZE
+        # reserve for the size of the spare metadata volume,
+        # used for metadata check and repair
+        size_bytes -= POOL_METADATA_SIZE
+        # round down to a whole extent
         size_bytes -= size_bytes % PHYSICAL_EXTENT_BYTES
+        # reduce for metadata overhead
         size_bytes -= PHYSICAL_EXTENT_BYTES
     dev_path = '/dev/%s' % devname
     grow_vols = find_grow_vols(opts, devices, group, size_bytes)
@@ -562,8 +565,7 @@ def main(argv):
             'lvextend',
             '--poolmetadatasize',
             '+%sB' % POOL_METADATA_SIZE,
-            thin_pool,
-            dev_path
+            '%s/%s' % (group, thin_pool_name)
         ], 'Add %s to thin pool metadata %s' % (
             convert_bytes(POOL_METADATA_SIZE), thin_pool)))
         commands.append(Command([
diff --git a/diskimage_builder/elements/growvols/tests/test_growvols.py b/diskimage_builder/elements/growvols/tests/test_growvols.py
index e45c652a..5817b6de 100644
--- a/diskimage_builder/elements/growvols/tests/test_growvols.py
+++ b/diskimage_builder/elements/growvols/tests/test_growvols.py
@@ -433,14 +433,14 @@ class TestGrowvols(base.BaseTestCase):
     def test_find_thin_pool(self, mock_execute):
         # No thin pool
         mock_execute.return_value = LVS
-        self.assertIsNone(growvols.find_thin_pool(DEVICES, 'vg'))
+        self.assertEqual((None, None), growvols.find_thin_pool(DEVICES, 'vg'))
         mock_execute.assert_called_once_with([
             'lvs', '--noheadings', '--options',
             'lv_name,lv_dm_path,lv_attr,pool_lv'])
 
         # One thin pool, all volumes use it
         mock_execute.return_value = LVS_THIN
-        self.assertEqual('/dev/mapper/vg-lv_thinpool',
+        self.assertEqual(('/dev/mapper/vg-lv_thinpool', 'lv_thinpool'),
                          growvols.find_thin_pool(DEVICES, 'vg'))
 
         # One pool, not used by all volumes
@@ -621,14 +621,14 @@ class TestGrowvols(base.BaseTestCase):
             mock.call(['pvcreate', '/dev/sda5']),
             mock.call(['vgextend', 'vg', '/dev/sda5']),
             mock.call(['lvextend', '--poolmetadatasize', '+1073741824B',
+                       'vg/lv_thinpool']),
+            mock.call(['lvextend', '-L+207253143552B',
                        '/dev/mapper/vg-lv_thinpool', '/dev/sda5']),
-            mock.call(['lvextend', '-L+208326885376B',
-                       '/dev/mapper/vg-lv_thinpool', '/dev/sda5']),
-            mock.call(['lvextend', '--size', '+41662021632B',
+            mock.call(['lvextend', '--size', '+41448112128B',
                        '/dev/mapper/vg-lv_home']),
-            mock.call(['lvextend', '--size', '+83328237568B',
+            mock.call(['lvextend', '--size', '+82900418560B',
                        '/dev/mapper/vg-lv_var']),
-            mock.call(['lvextend', '--size', '+83336626176B',
+            mock.call(['lvextend', '--size', '+82904612864B',
                        '/dev/mapper/vg-lv_root']),
             mock.call(['xfs_growfs', '/dev/mapper/vg-lv_home']),
             mock.call(['xfs_growfs', '/dev/mapper/vg-lv_var']),