--- lib/prometheus_exporter/instrumentation/active_record.rb.orig	2020-10-05 19:06:08.912325451 -0300
+++ lib/prometheus_exporter/instrumentation/active_record.rb	2020-10-05 19:06:12.229036702 -0300
@@ -69,7 +69,7 @@
 
         labels_from_config = pool.spec.config
           .select { |k, v| @config_labels.include? k }
-          .map { |k, v| [k.to_s.prepend("dbconfig_"), v] }
+          .map { |k, v| [k.to_s.dup.prepend("dbconfig_"), v] }
 
         labels = @metric_labels.merge(pool_name: pool.spec.name).merge(Hash[labels_from_config])