diff --git a/test/functional/interface_rest.py b/test/functional/interface_rest.py
index 6b4bb7970f7..2e9617d0c20 100755
--- a/test/functional/interface_rest.py
+++ b/test/functional/interface_rest.py
@@ -489,7 +489,11 @@ class RESTTest (BitcoinTestFramework):
             get_block_part(status=400, query_params={"offset": len(block_bin) + 1, "size": 1})
             get_block_part(status=400, query_params={"offset": 0, "size": len(block_bin) + 1})
 
-        self.test_rest_request(f"/blockpart/{blockhash}", status=400, req_type=ReqType.JSON, ret_type=RetType.OBJ)
+        res = self.test_rest_request(f"/blockpart/{blockhash}", status=400, req_type=ReqType.BIN, ret_type=RetType.OBJ)
+        assert res.read().decode().startswith("Block part offset missing or invalid")
+
+        res = self.test_rest_request(f"/blockpart/{blockhash}", query_params={"offset":0, "size":1}, status=400, req_type=ReqType.JSON, ret_type=RetType.OBJ)
+        assert res.read().decode().startswith("JSON output is not supported for this request type")
 
         self.log.info("Missing block data should cause REST API to fail")