diff --git a/src/modelarrayio/storage/tiledb_storage.py b/src/modelarrayio/storage/tiledb_storage.py
index 98e8e0d..7ca212b 100644
--- a/src/modelarrayio/storage/tiledb_storage.py
+++ b/src/modelarrayio/storage/tiledb_storage.py
@@ -14,6 +14,9 @@
 
 logger = logging.getLogger(__name__)
 
+# TileDBArray R package expects dimensions to be R integers.
+_DIM_DTYPE = np.int32
+
 
 def resolve_dtype(storage_dtype):
     """Resolve a storage dtype to a supported NumPy floating type.
@@ -162,10 +165,10 @@ def create_scalar_matrix_array(
 
     # Domain and schema
     dim_subjects = tiledb.Dim(
-        name='subjects', domain=(0, n_files - 1), tile=tile_shape[0], dtype=np.int64
+        name='subjects', domain=(0, n_files - 1), tile=tile_shape[0], dtype=_DIM_DTYPE
     )
     dim_items = tiledb.Dim(
-        name='items', domain=(0, n_elements - 1), tile=tile_shape[1], dtype=np.int64
+        name='items', domain=(0, n_elements - 1), tile=tile_shape[1], dtype=_DIM_DTYPE
     )
     dom = tiledb.Domain(dim_subjects, dim_items)
     attr_filters = _build_filter_list(compression, compression_level, shuffle)
@@ -254,10 +257,10 @@ def create_empty_scalar_matrix_array(
     _ensure_parent_group(uri)
 
     dim_subjects = tiledb.Dim(
-        name='subjects', domain=(0, n_files - 1), tile=tile_shape[0], dtype=np.int64
+        name='subjects', domain=(0, n_files - 1), tile=tile_shape[0], dtype=_DIM_DTYPE
     )
     dim_items = tiledb.Dim(
-        name='items', domain=(0, n_elements - 1), tile=tile_shape[1], dtype=np.int64
+        name='items', domain=(0, n_elements - 1), tile=tile_shape[1], dtype=_DIM_DTYPE
     )
     dom = tiledb.Domain(dim_subjects, dim_items)
     attr_filters = _build_filter_list(compression, compression_level, shuffle)
@@ -349,7 +352,7 @@ def write_parcel_names(base_uri: str, array_path: str, names: Sequence[str]):
 
     n = len(names)
     dim_idx = tiledb.Dim(
-        name='idx', domain=(0, max(n - 1, 0)), tile=max(1, min(n, 1024)), dtype=np.int64
+        name='idx', domain=(0, max(n - 1, 0)), tile=max(1, min(n, 1024)), dtype=_DIM_DTYPE
     )
     dom = tiledb.Domain(dim_idx)
     # np.unicode_ was removed in NumPy 2.0; np.str_ is the compatible string scalar.
@@ -383,7 +386,7 @@ def write_column_names(base_uri: str, scalar: str, sources: Sequence[str]):
 
     n = len(sources)
     dim_idx = tiledb.Dim(
-        name='idx', domain=(0, max(n - 1, 0)), tile=max(1, min(n, 1024)), dtype=np.int64
+        name='idx', domain=(0, max(n - 1, 0)), tile=max(1, min(n, 1024)), dtype=_DIM_DTYPE
     )
     dom = tiledb.Domain(dim_idx)
     attr_values = tiledb.Attr(name='values', dtype=np.str_)
diff --git a/test/test_tiledb_storage.py b/test/test_tiledb_storage.py
index 603e80e..5ed4d31 100644
--- a/test/test_tiledb_storage.py
+++ b/test/test_tiledb_storage.py
@@ -12,6 +12,11 @@
 from modelarrayio.storage import tiledb_storage
 
 
+def assert_domain_dtypes(array: tiledb.Array, expected: list[str]) -> None:
+    for idx, dtype in enumerate(expected):
+        assert array.schema.domain.dim(idx).dtype == np.dtype(dtype)
+
+
 def test_build_filter_list_variants() -> None:
     no_filters = tiledb_storage._build_filter_list(None, None, shuffle=False)
     assert isinstance(no_filters, tiledb.FilterList)
@@ -41,6 +46,7 @@ def test_create_empty_scalar_matrix_array_writes_metadata_and_overwrites(tmp_pat
     )
     assert tiledb.object_type(uri) == 'array'
     with tiledb.open(uri, 'r') as array:
+        assert_domain_dtypes(array, ['int32', 'int32'])
         assert json.loads(array.meta['column_names']) == ['s1', 's2']
 
     uri_again = tiledb_storage.create_empty_scalar_matrix_array(
@@ -96,6 +102,7 @@ def test_write_parcel_names_and_column_names(tmp_path: Path) -> None:
     parcel_uri = base / 'parcels' / 'parcel_id'
     assert tiledb.object_type(str(parcel_uri)) == 'array'
     with tiledb.open(str(parcel_uri), 'r') as array:
+        assert_domain_dtypes(array, ['int32'])
         np.testing.assert_array_equal(array[:]['values'], np.array(['P1', 'P2'], dtype=object))
 
     # Some TileDB builds do not implicitly create missing parent directories.
@@ -104,6 +111,7 @@ def test_write_parcel_names_and_column_names(tmp_path: Path) -> None:
     tiledb_storage.write_column_names(str(base), 'FA', ['sub-1', 'sub-2'])
     column_uri = base / 'scalars' / 'FA' / 'column_names'
     with tiledb.open(str(column_uri), 'r') as array:
+        assert_domain_dtypes(array, ['int32'])
         np.testing.assert_array_equal(
             array[:]['values'], np.array(['sub-1', 'sub-2'], dtype=object)
         )
@@ -124,5 +132,6 @@ def test_create_scalar_matrix_array_writes_values_and_metadata(tmp_path: Path) -
         compression_level=3,
     )
     with tiledb.open(uri, 'r') as array:
+        assert_domain_dtypes(array, ['int32', 'int32'])
         np.testing.assert_array_equal(array[:]['values'], values)
         assert json.loads(array.meta['column_names']) == ['first', 'second']