diff --git a/tiled/server/pydantic_sparse.py b/tiled/server/pydantic_sparse.py
index 8785daddc..7d6113e2d 100644
--- a/tiled/server/pydantic_sparse.py
+++ b/tiled/server/pydantic_sparse.py
@@ -2,7 +2,7 @@
 
 import pydantic
 
-from ..structures.array import BuiltinDtype, StructDtype, Endianness, Kind
+from ..structures.array import BuiltinDtype, Endianness, Kind, StructDtype
 from ..structures.sparse import SparseLayout
 
 
@@ -10,7 +10,9 @@ class COOStructure(pydantic.BaseModel):
     shape: Tuple[int, ...]  # tuple of ints like (3, 3)
     chunks: Tuple[Tuple[int, ...], ...]  # tuple-of-tuples-of-ints like ((3,), (3,))
     data_type: Optional[Union[BuiltinDtype, StructDtype]] = None
-    coord_data_type: BuiltinDtype = BuiltinDtype(Endianness("little"), Kind("u"), 8)   # numpy 'uint' dtype
+    coord_data_type: Optional[BuiltinDtype] = BuiltinDtype(
+        Endianness("little"), Kind("u"), 8
+    )  # numpy 'uint' dtype
     dims: Optional[Tuple[str, ...]] = None  # None or tuple of names like ("x", "y")
     resizable: Union[bool, Tuple[bool, ...]] = False
     layout: SparseLayout = SparseLayout.COO
diff --git a/tiled/structures/sparse.py b/tiled/structures/sparse.py
index 13a8c2bcd..a84e67499 100644
--- a/tiled/structures/sparse.py
+++ b/tiled/structures/sparse.py
@@ -2,7 +2,7 @@
 from dataclasses import dataclass
 from typing import Optional, Tuple, Union
 
-from .array import BuiltinDtype, StructDtype, Endianness, Kind
+from .array import BuiltinDtype, Endianness, Kind, StructDtype
 
 
 class SparseLayout(str, enum.Enum):
@@ -16,7 +16,9 @@ class COOStructure:
     chunks: Tuple[Tuple[int, ...], ...]  # tuple-of-tuples-of-ints like ((3,), (3,))
     shape: Tuple[int, ...]  # tuple of ints like (3, 3)
     data_type: Optional[Union[BuiltinDtype, StructDtype]] = None
-    coord_data_type: BuiltinDtype = BuiltinDtype(Endianness("little"), Kind("u"), 8)   # numpy 'uint' dtype
+    coord_data_type: Optional[BuiltinDtype] = BuiltinDtype(
+        Endianness("little"), Kind("u"), 8
+    )  # numpy 'uint' dtype
     dims: Optional[Tuple[str, ...]] = None  # None or tuple of names like ("x", "y")
     resizable: Union[bool, Tuple[bool, ...]] = False
     layout: SparseLayout = SparseLayout.COO
@@ -29,7 +31,9 @@ def from_json(cls, structure):
             data_type = StructDtype.from_json(data_type)
         else:
             data_type = BuiltinDtype.from_json(data_type)
-        coord_data_type = structure.get("coord_data_type", {"endianness":"little", "kind":"u", "itemsize":8})
+        coord_data_type = structure.get(
+            "coord_data_type", {"endianness": "little", "kind": "u", "itemsize": 8}
+        )
         return cls(
             data_type=data_type,
             coord_data_type=BuiltinDtype.from_json(coord_data_type),