diff --git a/app/api/formsemestres.py b/app/api/formsemestres.py
index 87a640194..3aaef1c78 100644
--- a/app/api/formsemestres.py
+++ b/app/api/formsemestres.py
@@ -565,7 +565,9 @@ def save_groups_auto_assignment(formsemestre_id: int):
 @permission_required(Permission.ScoView)
 @as_json
 def formsemestre_edt(formsemestre_id: int):
-    """l'emploi du temps du semestre"""
+    """l'emploi du temps du semestre
+    Si ok, une liste d'évènements. Sinon, une chaine indiquant un message d'erreur.
+    """
     query = FormSemestre.query.filter_by(id=formsemestre_id)
     if g.scodoc_dept:
         query = query.filter_by(dept_id=g.scodoc_dept_id)
diff --git a/app/scodoc/sco_edt_cal.py b/app/scodoc/sco_edt_cal.py
index 0c7f89b44..7d63add01 100644
--- a/app/scodoc/sco_edt_cal.py
+++ b/app/scodoc/sco_edt_cal.py
@@ -58,13 +58,31 @@ def formsemestre_load_calendar(
     try:
         with open(ics_filename, "rb") as file:
             log(f"Loading edt from {ics_filename}")
-            calendar = icalendar.Calendar.from_ical(file.read())
-    except FileNotFoundError:
-        flash("erreur chargement du calendrier")
+            try:
+                calendar = icalendar.Calendar.from_ical(file.read())
+            except ValueError as exc:
+                log(
+                    f"""formsemestre_load_calendar: error importing ics for {
+                        formsemestre}\npath='{ics_filename}'"""
+                )
+                raise ScoValueError(
+                    f"calendrier ics illisible (edt_id={edt_id})"
+                ) from exc
+    except FileNotFoundError as exc:
         log(
             f"formsemestre_load_calendar: ics not found for {formsemestre}\npath='{ics_filename}'"
         )
-        return None
+        raise ScoValueError(
+            f"Fichier ics introuvable (filename={ics_filename})"
+        ) from exc
+    except PermissionError as exc:
+        log(
+            f"""formsemestre_load_calendar: permission denied for {formsemestre
+                                                                 }\npath='{ics_filename}'"""
+        )
+        raise ScoValueError(
+            f"Fichier ics inaccessible: vérifier permissions (filename={ics_filename})"
+        ) from exc
 
     return calendar
 
@@ -88,7 +106,10 @@ def formsemestre_edt_dict(formsemestre: FormSemestre) -> list[dict]:
     Fonction appellée par l'API /formsemestre/<int:formsemestre_id>/edt
     TODO: spécifier intervalle de dates start et end
     """
-    events_scodoc = _load_and_convert_ics(formsemestre)
+    try:
+        events_scodoc = _load_and_convert_ics(formsemestre)
+    except ScoValueError as exc:
+        return exc.args[0]
     # Génération des événements pour le calendrier html
     events_cal = []
     for event in events_scodoc:
diff --git a/app/templates/formsemestre/edt.j2 b/app/templates/formsemestre/edt.j2
index 2dbdaadb1..d5bb1debf 100644
--- a/app/templates/formsemestre/edt.j2
+++ b/app/templates/formsemestre/edt.j2
@@ -95,7 +95,12 @@ document.addEventListener('DOMContentLoaded', function() {
     fetch(`${SCO_URL}/../api/formsemestre/{{formsemestre.id}}/edt`)
 		.then(r=>{return r.json()})
 		.then(events=>{
-            calendar.createEvents(events);
+            if (typeof events == 'string') {
+                // error !
+                alert("error: " + events)
+            } else {
+                calendar.createEvents(events);
+            }
         });
 });
 
diff --git a/sco_version.py b/sco_version.py
index 1fd49c111..e8ed7d5f8 100644
--- a/sco_version.py
+++ b/sco_version.py
@@ -1,7 +1,7 @@
 # -*- mode: python -*-
 # -*- coding: utf-8 -*-
 
-SCOVERSION = "9.6.53"
+SCOVERSION = "9.6.54"
 
 SCONAME = "ScoDoc"