diff --git a/clinica/iotools/bids_utils.py b/clinica/iotools/bids_utils.py
index e68d58822..ad51a5e8c 100644
--- a/clinica/iotools/bids_utils.py
+++ b/clinica/iotools/bids_utils.py
@@ -360,7 +360,7 @@ def create_participants_df(
 
     fields_bids = ["participant_id"]
     prev_location = ""
-    prev_sheet = None
+    prev_sheet = 0
     index_to_drop = []
     subjects_to_drop = []
     study_name = StudyName(study_name)