diff --git a/src/azul/plugins/metadata/anvil/indexer/transform.py b/src/azul/plugins/metadata/anvil/indexer/transform.py
index a57b85a65b..34f5e5d4d6 100644
--- a/src/azul/plugins/metadata/anvil/indexer/transform.py
+++ b/src/azul/plugins/metadata/anvil/indexer/transform.py
@@ -35,6 +35,9 @@
 from azul import (
     JSON,
 )
+from azul.collections import (
+    deep_dict_merge,
+)
 from azul.indexer import (
     BundleFQID,
     BundlePartition,
@@ -428,7 +431,21 @@ def reconcile_inner_entities(cls,
                                  ) -> tuple[JSON, BundleFQID]:
         this_entity, this_bundle = this
         that_entity, that_bundle = that
-        return that if that_bundle.version > this_bundle.version else this
+        if this_entity.keys() == that_entity.keys():
+            return that if that_bundle.version > this_bundle.version else this
+        else:
+            assert entity_type == 'datasets', (entity_type, this, that)
+            assert this_bundle.version == that_bundle.version, (this, that)
+            expected_keys = cls.field_types()[entity_type].keys()
+            assert this_entity.keys() < expected_keys, this
+            assert that_entity.keys() < expected_keys, that
+            merged = deep_dict_merge((this_entity, that_entity))
+            # Confirm that we combined a regular dataset with a DUOS stub to
+            # produce the complete set of expected fields
+            assert merged.keys() == expected_keys, (this, that)
+            # We can safely discard that_bundle because only the version is
+            # used by the caller, and we know the versions are equal.
+            return merged, this_bundle
 
 
 class ActivityTransformer(BaseTransformer):