diff --git a/python/lsst/daf/butler/_dataset_type.py b/python/lsst/daf/butler/_dataset_type.py
index e9ba515ef9..c7b546cc94 100644
--- a/python/lsst/daf/butler/_dataset_type.py
+++ b/python/lsst/daf/butler/_dataset_type.py
@@ -676,7 +676,7 @@ def to_simple(self, minimal: bool = False) -> SerializedDatasetType:
                 "name": self.name,
                 "storageClass": self._storageClassName,
                 "isCalibration": self._isCalibration,
-                "dimensions": list(self._dimensions.required),
+                "dimensions": list(self._dimensions.names),
             }
 
             if self._parentStorageClassName is not None:
diff --git a/python/lsst/daf/butler/dimensions/_coordinate.py b/python/lsst/daf/butler/dimensions/_coordinate.py
index d511a49cac..d6f4189e9c 100644
--- a/python/lsst/daf/butler/dimensions/_coordinate.py
+++ b/python/lsst/daf/butler/dimensions/_coordinate.py
@@ -709,7 +709,7 @@ def to_simple(self, minimal: bool = False) -> SerializedDataCoordinate:
         else:
             records = None
 
-        return SerializedDataCoordinate(dataId=dict(self.required), records=records)
+        return SerializedDataCoordinate(dataId=dict(self.mapping), records=records)
 
     @classmethod
     def from_simple(
diff --git a/python/lsst/daf/butler/tests/butler_queries.py b/python/lsst/daf/butler/tests/butler_queries.py
index 0410afcef5..64aaa1bbb8 100644
--- a/python/lsst/daf/butler/tests/butler_queries.py
+++ b/python/lsst/daf/butler/tests/butler_queries.py
@@ -303,6 +303,18 @@ def test_simple_dataset_query(self) -> None:
             butler.query_datasets("bias", "*", detector=100, instrument="Unknown", find_first=False)
         self.assertIn("doomed", str(cm2.exception))
 
+        # Test for a regression of an issue where "band" was not being included
+        # in the data ID, despite being one of the dimensions in the "flat"
+        # dataset type.
+        refs = butler.query_datasets("flat", "imported_r", where="detector = 2", instrument="Cam1")
+        self.assertEqual(len(refs), 1)
+        flat = refs[0]
+        self.assertEqual(flat.datasetType.name, "flat")
+        self.assertEqual(flat.dataId["instrument"], "Cam1")
+        self.assertEqual(flat.dataId["detector"], 2)
+        self.assertEqual(flat.dataId["physical_filter"], "Cam1-R1")
+        self.assertEqual(flat.dataId["band"], "r")
+
     def test_general_query(self) -> None:
         """Test Query.general and its result."""
         butler = self.make_butler("base.yaml", "datasets.yaml")