diff --git a/apis/python/src/tiledbsoma/_dataframe.py b/apis/python/src/tiledbsoma/_dataframe.py
index c380fd20c5..dee770a08d 100644
--- a/apis/python/src/tiledbsoma/_dataframe.py
+++ b/apis/python/src/tiledbsoma/_dataframe.py
@@ -520,8 +520,8 @@ def _upgrade_or_change_domain_helper(
         dim_schema = pa.schema(dim_schema_list)
 
         # Convert the user's tuple of low/high pairs into a dict keyed by index-column name.
-        new_domain_dict: Dict[str, Iterable[Any]] = {}
-        for i, dim_name in enumerate(dim_names):
+        new_domain_dict: Dict[str, Domain] = {}
+        for dim_name, new_dom in zip(dim_names, newdomain):
             # Domain can't be specified for strings (core constraint) so let them keystroke that easily.
             if (
                 dim_schema.field(dim_name).type
@@ -531,11 +531,11 @@ def _upgrade_or_change_domain_helper(
                     pa.binary(),
                     pa.large_binary(),
                 ]
-                and newdomain[i] is None
+                and new_dom is None
             ):
                 new_domain_dict[dim_name] = ("", "")
             else:
-                new_domain_dict[dim_name] = tuple(newdomain[i])  # type: ignore
+                new_domain_dict[dim_name] = tuple(new_dom)  # type: ignore
 
         # Return this as a pyarrow table. This has n columns where n is the number of
         # index columns, and two rows: one row for the low values and one for the high values.