diff --git a/kiwi/builder/disk.py b/kiwi/builder/disk.py
index 6f17b6f1f93..5c6fdd7f8e9 100644
--- a/kiwi/builder/disk.py
+++ b/kiwi/builder/disk.py
@@ -74,22 +74,28 @@
     KiwiVolumeManagerSetupError
 )
 
-StorageMap = TypedDict(
-    'StorageMap', {
-        'system': Optional[Union[FileSystemBase, VolumeManagerBase]],
-        'system_boot': Optional[FileSystemBase],
-        'system_efi': Optional[FileSystemBase],
-        'system_spare': Optional[FileSystemBase],
-        'system_custom_parts': Dict[str, FileSystemBase],
-        'luks_root': Optional[LuksDevice],
-        'raid_root': Optional[RaidDevice],
-        'integrity_root': Optional[IntegrityDevice]
-    }
-)
-
 log = logging.getLogger('kiwi')
 
 
+class StorageMap(TypedDict):
+    system: \
+        Optional[Union[FileSystemBase, VolumeManagerBase]]
+    system_boot: \
+        Optional[FileSystemBase]
+    system_efi: \
+        Optional[FileSystemBase]
+    system_spare: \
+        Optional[FileSystemBase]
+    system_custom_parts: \
+        Dict[str, FileSystemBase]
+    luks_root: \
+        Optional[LuksDevice]
+    raid_root: \
+        Optional[RaidDevice]
+    integrity_root: \
+        Optional[IntegrityDevice]
+
+
 class DiskBuilder:
     """
     **Disk image builder**