diff --git a/docker-compose/tango-prometheus-exporter/code/tango-prometheus-client.py b/docker-compose/tango-prometheus-exporter/code/tango-prometheus-client.py
index 18eca65bd4bf2ed4e3efa16e2993ddd49b4b9b52..3152ca29c8c0d78846508e8301e259e694579e75 100644
--- a/docker-compose/tango-prometheus-exporter/code/tango-prometheus-client.py
+++ b/docker-compose/tango-prometheus-exporter/code/tango-prometheus-client.py
@@ -97,7 +97,7 @@ class CustomCollector(object):
             return None
 
         # (labels, value)
-        return ([dev.dev_name(), attr_info.name, str_value, data_type, f"{x:02}", f"{y:02}", f"{idx:03}"]], float_value)
+        return ([dev.dev_name(), attr_info.name, str_value, data_type, f"{x:02}", f"{y:02}", f"{idx:03}"], float_value)
 
     def metrics_scalar(self, dev, attr_info, attr_value):
         """ Return all metrics for a given SCALAR attribute. """