diff --git a/app/scodoc/sco_bulletins.py b/app/scodoc/sco_bulletins.py
index de7f28c9d..ca6748de7 100644
--- a/app/scodoc/sco_bulletins.py
+++ b/app/scodoc/sco_bulletins.py
@@ -1013,11 +1013,16 @@ def mail_bulletin(formsemestre_id, I, pdfdata, filename, recipient_addr):
     intro_mail = sco_preferences.get_preference("bul_intro_mail", formsemestre_id)
 
     if intro_mail:
-        hea = intro_mail % {
-            "nomprenom": etud["nomprenom"],
-            "dept": dept,
-            "webmaster": webmaster,
-        }
+        try:
+            hea = intro_mail % {
+                "nomprenom": etud["nomprenom"],
+                "dept": dept,
+                "webmaster": webmaster,
+            }
+        except KeyError as e:
+            raise ScoValueError(
+                "format 'Message d'accompagnement' (bul_intro_mail) invalide, revoir les réglages dans les préférences"
+            )
     else:
         hea = ""