diff --git a/cdisc_rules_engine/utilities/dataset_preprocessor.py b/cdisc_rules_engine/utilities/dataset_preprocessor.py
index f1ebc647c..0eb2f8356 100644
--- a/cdisc_rules_engine/utilities/dataset_preprocessor.py
+++ b/cdisc_rules_engine/utilities/dataset_preprocessor.py
@@ -162,7 +162,9 @@ def preprocess(  # noqa
                         right_dataset_domain_details=domain_details,
                         datasets=datasets,
                     )
-                    merged_domains.add(file_info.domain)
+                    merged_domains.add(
+                        file_info.domain if file_info.domain else file_info.name
+                    )
         return result
 
     def _find_parent_dataset(