diff --git a/cdisc_rules_engine/utilities/data_processor.py b/cdisc_rules_engine/utilities/data_processor.py
index 04d6dbe46..82c9d6c22 100644
--- a/cdisc_rules_engine/utilities/data_processor.py
+++ b/cdisc_rules_engine/utilities/data_processor.py
@@ -17,6 +17,7 @@
     DataServiceFactory,
     DummyDataService,
 )
+from cdisc_rules_engine.exceptions.custom_exceptions import PreprocessingError
 from cdisc_rules_engine.utilities.utils import (
     search_in_list_of_dicts,
 )
@@ -331,7 +332,7 @@ def _merge_supp_with_multiple_idvars(
             validation_keys.append(idvar_for_qnam)
             grouped = qnam_check.groupby(validation_keys).size()
             if (grouped > 1).any():
-                raise ValueError(
+                raise PreprocessingError(
                     f"Multiple records with the same QNAM '{qnam}' match a single parent record"
                 )
         return result_dataset
@@ -351,14 +352,20 @@ def process_supp(supp_dataset):
         columns_to_drop = [
             col for col in ["QNAM", "QVAL", "QLABEL"] if col in supp_dataset.columns
         ]
-        if "RDOMAIN" in supp_dataset.columns and supp_dataset["RDOMAIN"][0] == "DM":
-            excluded_columns = list(supp_dataset["QNAM"].unique()) + columns_to_drop
-            group_cols = [c for c in supp_dataset.columns if c not in excluded_columns]
-            supp_dataset = PandasDataset(
-                supp_dataset.data.groupby(group_cols, dropna=False, as_index=False).agg(
-                    lambda x: (x.dropna().iloc[0] if not x.dropna().empty else pd.NA)
-                )
+        excluded_columns = list(supp_dataset["QNAM"].unique()) + columns_to_drop
+        group_cols = [c for c in supp_dataset.columns if c not in excluded_columns]
+        grouped = supp_dataset.data.groupby(
+            group_cols + ["QNAM"], dropna=False, as_index=False
+        ).size()
+        if (grouped["size"] > 1).any():
+            raise PreprocessingError(
+                "Multiple records with the same QNAM match a single parent record"
+            )
+        supp_dataset = PandasDataset(
+            supp_dataset.data.groupby(group_cols, dropna=False, as_index=False).agg(
+                lambda x: (x.dropna().iloc[0] if not x.dropna().empty else pd.NA)
             )
+        )
         if columns_to_drop:
             supp_dataset = supp_dataset.drop(labels=columns_to_drop, axis=1)
         return supp_dataset
@@ -377,7 +384,7 @@ def _validate_qnam(
                 continue
             grouped = qnam_check.groupby(common_keys).size()
             if (grouped > 1).any():
-                raise ValueError(
+                raise PreprocessingError(
                     f"Multiple records with the same QNAM '{qnam}' match a single parent record"
                 )
 
@@ -397,7 +404,7 @@ def _validate_qnam_dask(
             problem_groups = grouped_counts[grouped_counts > 1]
             problem_groups_computed = problem_groups.compute()
             if len(problem_groups_computed) > 0:
-                raise ValueError(
+                raise PreprocessingError(
                     f"Multiple records with the same QNAM '{qnam}' match a single parent record. "
                 )
 
diff --git a/tests/unit/test_dataset_preprocessor.py b/tests/unit/test_dataset_preprocessor.py
index 2b238ce9d..de6a1ce57 100644
--- a/tests/unit/test_dataset_preprocessor.py
+++ b/tests/unit/test_dataset_preprocessor.py
@@ -17,7 +17,6 @@
 from cdisc_rules_engine.models.library_metadata_container import (
     LibraryMetadataContainer,
 )
-
 from cdisc_rules_engine.models.dataset import PandasDataset
 
 
diff --git a/tests/unit/test_merge_supp_datasets.py b/tests/unit/test_merge_supp_datasets.py
index 370bdb728..55f438928 100644
--- a/tests/unit/test_merge_supp_datasets.py
+++ b/tests/unit/test_merge_supp_datasets.py
@@ -7,6 +7,7 @@
 from cdisc_rules_engine.utilities.data_processor import DataProcessor
 import pandas as pd
 import pandas.testing as pdt
+from cdisc_rules_engine.exceptions.custom_exceptions import PreprocessingError
 
 
 @pytest.fixture
@@ -55,6 +56,30 @@ def test_process_supp():
     assert "QLABEL" not in processed_dataset.data.columns, "'QVAL' should be dropped."
 
 
+def test_data_processor_suppae_multiple_qnams():
+    suppae_data = {
+        "STUDYID": ["CDISCPILOT01", "CDISCPILOT01"],
+        "RDOMAIN": ["AE", "AE"],
+        "USUBJID": ["CDISC008", "CDISC008"],
+        "IDVAR": ["", ""],
+        "IDVARVAL": ["", ""],
+        "QNAM": ["AESPID", "AEREL2"],
+        "QLABEL": ["Sponsor ID", "Relationship 2"],
+        "QVAL": ["SP001", "POSSIBLE"],
+        "QORIG": ["CRF", "CRF"],
+        "QEVAL": ["", ""],
+    }
+    suppae_ds = PandasDataset(pd.DataFrame(suppae_data))
+    assert suppae_ds.data.shape[0] == 2
+
+    result = DataProcessor().process_supp(suppae_ds).data
+
+    assert result.shape[0] == 1
+    assert {"AESPID", "AEREL2"}.issubset(set(result.columns))
+    assert result.loc[0, "AESPID"] == "SP001"
+    assert result.loc[0, "AEREL2"] == "POSSIBLE"
+
+
 @patch.object(LocalDataService, "check_filepath", return_value=False)
 @patch.object(LocalDataService, "_async_get_datasets")
 def test_merge_pivot_supp_dataset(
@@ -258,7 +283,7 @@ def test_merge_supp_dataset_multi_idvar_aggregation(
 
 @patch.object(LocalDataService, "check_filepath", return_value=False)
 @patch.object(LocalDataService, "_async_get_datasets")
-def test_merge_supp_dataset_multi_idvar_same_qnam_validation_error(
+def test_merge_supp_dataset_same_qnam_validation_error(
     mock_async_get_datasets, data_service
 ):
     parent_dataset = PandasDataset(
@@ -292,7 +317,7 @@ def test_merge_supp_dataset_multi_idvar_same_qnam_validation_error(
 
     mock_async_get_datasets.return_value = [parent_dataset, supp_dataset]
 
-    with pytest.raises(ValueError, match="Multiple records with the same QNAM"):
+    with pytest.raises(PreprocessingError, match="Multiple records with the same QNAM"):
         DataProcessor.merge_pivot_supp_dataset(
             data_service.dataset_implementation, parent_dataset, supp_dataset
         )