diff --git a/app/api/partitions.py b/app/api/partitions.py
index b31ff80d..1f5ef8a1 100644
--- a/app/api/partitions.py
+++ b/app/api/partitions.py
@@ -92,7 +92,7 @@ def formsemestre_partitions(formsemestre_id: int):
     formsemestre: FormSemestre = query.first_or_404(formsemestre_id)
     partitions = sorted(formsemestre.partitions, key=attrgetter("numero"))
     return {
-        partition.id: partition.to_dict(with_groups=True)
+        str(partition.id): partition.to_dict(with_groups=True, str_keys=True)
         for partition in partitions
         if partition.partition_name is not None
     }
diff --git a/app/models/groups.py b/app/models/groups.py
index 5c9ae168..1d07ed21 100644
--- a/app/models/groups.py
+++ b/app/models/groups.py
@@ -85,8 +85,10 @@ class Partition(db.Model):
         "Vrai s'il s'agit de la partition de parcours"
         return self.partition_name == scu.PARTITION_PARCOURS
 
-    def to_dict(self, with_groups=False) -> dict:
-        """as a dict, with or without groups"""
+    def to_dict(self, with_groups=False, str_keys: bool = False) -> dict:
+        """as a dict, with or without groups.
+        If str_keys, convert integer dict keys to strings (useful for JSON)
+        """
         d = dict(self.__dict__)
         d["partition_id"] = self.id
         d.pop("_sa_instance_state", None)
@@ -95,9 +97,15 @@ class Partition(db.Model):
         if with_groups:
             groups = sorted(self.groups, key=attrgetter("numero", "group_name"))
             # un dict et non plus une liste, pour JSON
-            d["groups"] = {
-                group.id: group.to_dict(with_partition=False) for group in groups
-            }
+            if str_keys:
+                d["groups"] = {
+                    str(group.id): group.to_dict(with_partition=False)
+                    for group in groups
+                }
+            else:
+                d["groups"] = {
+                    group.id: group.to_dict(with_partition=False) for group in groups
+                }
         return d
 
     def get_etud_group(self, etudid: int) -> "GroupDescr":