diff --git a/euphrosyne/assets/js/web-components/open-theso-type-ahead.ts b/euphrosyne/assets/js/web-components/open-theso-type-ahead.ts
index 019e00373..1b9430bd5 100644
--- a/euphrosyne/assets/js/web-components/open-theso-type-ahead.ts
+++ b/euphrosyne/assets/js/web-components/open-theso-type-ahead.ts
@@ -26,7 +26,9 @@ export abstract class OpenThesoTypeAhead extends TypeAheadList {
       // autocomplete
       url = `https://opentheso.huma-num.fr/opentheso/openapi/v1/concept/${this.thesorusId}/autocomplete/${q}?lang=fr&exactMatch=false`;
     }
-    const response = await fetch(url);
+    const response = await fetch(url, {
+      headers: { Accept: "application/json" },
+    });
 
     if (response && response.status === 404) {
       return [];
diff --git a/lab/tests/test_opentheso.py b/lab/tests/test_opentheso.py
index 6ad71e70e..71c6c9987 100644
--- a/lab/tests/test_opentheso.py
+++ b/lab/tests/test_opentheso.py
@@ -15,6 +15,7 @@ def test_fetch_parent_ids_from_id(request_mock: mock.MagicMock):
     assert fetch_parent_ids_from_id("theso_id", "concept_id") == ["FIRST", "SECOND"]
     request_mock.get.assert_called_once_with(
         # pylint: disable=line-too-long
-        "https://opentheso.huma-num.fr/opentheso/openapi/v1/concept/theso_id/concept_id/expansion?way=top",
+        "https://opentheso.huma-num.fr/openapi/v1/concept/theso_id/concept_id/expansion?way=top",
+        headers={"Accept": "application/json"},
         timeout=5,
     )
diff --git a/lab/thesauri/opentheso.py b/lab/thesauri/opentheso.py
index b3f8b3d24..fd66b32b1 100644
--- a/lab/thesauri/opentheso.py
+++ b/lab/thesauri/opentheso.py
@@ -14,7 +14,8 @@ def fetch_parent_ids_from_id(theso_id: str, concept_id: str) -> list[str]:
     try:
         response = requests.get(
             # pylint: disable=line-too-long
-            f"https://opentheso.huma-num.fr/opentheso/openapi/v1/concept/{theso_id}/{concept_id}/expansion?way=top",
+            f"https://opentheso.huma-num.fr/openapi/v1/concept/{theso_id}/{concept_id}/expansion?way=top",
+            headers={"Accept": "application/json"},
             timeout=5,
         )
     except requests.exceptions.RequestException as e: