diff --git a/idc_index/index.py b/idc_index/index.py
index 0d113bc1..6390f50d 100644
--- a/idc_index/index.py
+++ b/idc_index/index.py
@@ -153,7 +153,7 @@ def _safe_filter_by_selection(
         patientId,
         studyInstanceUID,
         seriesInstanceUID,
-        sopInstanceUID=None,
+        sopInstanceUID,
         crdc_series_uuid,
     ):
         if collection_id is not None:
@@ -205,10 +205,10 @@ def _safe_filter_by_selection(
 
         if sopInstanceUID is not None:
             result_df = IDCClient._filter_by_dicom_instance_uid(
-                result_df, sopInstanceUID
+                df_index, sopInstanceUID
             )
             return result_df
-          
+
         if seriesInstanceUID is not None:
             result_df = IDCClient._filter_by_dicom_series_uid(
                 df_index, seriesInstanceUID
@@ -1512,6 +1512,7 @@ def citations_from_selection(
             patientId=patientId,
             studyInstanceUID=studyInstanceUID,
             seriesInstanceUID=seriesInstanceUID,
+            sopInstanceUID=None,
             crdc_series_uuid=None,
         )