diff --git a/app/views/absences.py b/app/views/absences.py
index 7120e990..24d972ee 100644
--- a/app/views/absences.py
+++ b/app/views/absences.py
@@ -1064,6 +1064,10 @@ def AddBilletAbsence(
     begin et end sont au format ISO (eg "1999-01-08 04:05:06")
     """
     t0 = time.time()
+    begin = str(begin)
+    end = str(end)
+    code_nip = str(code_nip) if code_nip else None
+
     # check etudid
     etuds = sco_etud.get_etud_info(etudid=etudid, code_nip=code_nip, filled=True)
     if not etuds: