diff --git a/lofar_station_client/requests/prometheus.py b/lofar_station_client/requests/prometheus.py
index 192cb90943a2ab8fb28e387ee041d5e7d7e1e411..0c61ace42a391e9895164e545e661f675aa61169 100644
--- a/lofar_station_client/requests/prometheus.py
+++ b/lofar_station_client/requests/prometheus.py
@@ -213,7 +213,7 @@ class PrometheusRequests:
 
         def ord_index(metric: dict) -> Tuple[str]:
             """Generate the ordered dict index from json metric"""
-            return (metric['x'], metric['y'])
+            return (metric["x"], metric["y"])
 
         result_dict = OrderedDict()
         for json_result in json_results:
diff --git a/tests/requests/test_prometheus.py b/tests/requests/test_prometheus.py
index 94cc0ea69fd47d539645becf5e16c8fd7a616e4e..e38d8068b1af6ee3f1a6e61de2c4ced82036831c 100644
--- a/tests/requests/test_prometheus.py
+++ b/tests/requests/test_prometheus.py
@@ -301,7 +301,7 @@ class PrometheusTest(base.TestCase):
 
         for result in reference_data["data"]["result"]:
             metric = result["metric"]
-            index = (metric['x'], metric['y'])
+            index = (metric["x"], metric["y"])
 
             result_dict_timestamps = [
                 result[0] for result in result_dict[index]["values"]