diff --git a/allensdk/brain_observatory/behavior/data_objects/stimuli/presentations.py b/allensdk/brain_observatory/behavior/data_objects/stimuli/presentations.py
index 879fbd4a6..eead6a477 100644
--- a/allensdk/brain_observatory/behavior/data_objects/stimuli/presentations.py
+++ b/allensdk/brain_observatory/behavior/data_objects/stimuli/presentations.py
@@ -571,7 +571,7 @@ def _check_for_errant_omitted_stimulus(
             first_row = input_df.iloc[0]
             if not pd.isna(first_row["omitted"]):
                 if first_row["omitted"]:
-                    input_df.drop(first_row.name, axis=0, inplace=True)
+                    input_df = input_df.drop(first_row.name, axis=0)
         return input_df
 
     @staticmethod