diff --git a/laborious/metrics.py b/laborious/metrics.py
index 9d422fb..796e159 100644
--- a/laborious/metrics.py
+++ b/laborious/metrics.py
@@ -30,12 +30,12 @@ PREDICTION_RESPONSE_TIME_MONITOR = Histogram(
 PREDICTION_OPC_WRITING_COUNT = Counter(
     "laborious_prediction_opc_writing_count",
     "Number of predictions written to the OPC server",
-    [CORE_LABELS, "opc_server_id"],
+    [*CORE_LABELS, "opc_server_id"],
 )
 
 PREDICTION_OPC_WRITING_RESPONSE_TIME_MONITOR = Histogram(
     "laborious_prediction_opc_writing_response_time_monitor",
     "Current response time of each prediction written to the OPC server",
-    [CORE_LABELS, "opc_server_id"],
+    [*CORE_LABELS, "opc_server_id"],
     buckets=[0.01, 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10.0]
 )