diff --git a/duniterpy/api/bma/blockchain.py b/duniterpy/api/bma/blockchain.py
index 8110cc67c2495853aec331154fb95449993d9fd9..cf3315c65ef7dd6365b9fc8e7d4386d321403e64 100644
--- a/duniterpy/api/bma/blockchain.py
+++ b/duniterpy/api/bma/blockchain.py
@@ -201,7 +201,7 @@ DIFFICULTIES_SCHEMA = {
         "block": {"type": "number"},
         "levels": {
             "type": "array",
-            "items": [
+            "prefixItems": [
                 {
                     "type": "object",
                     "properties": {