diff --git a/packages/lib/prometheus.js b/packages/lib/prometheus.js
index 9a9bda69..aaf34c11 100644
--- a/packages/lib/prometheus.js
+++ b/packages/lib/prometheus.js
@@ -275,6 +275,10 @@ function labelsToKey(labels, metricLabels) {
 		}
 	}
 
+	if (items.length === 1) {
+		return items[0];
+	}
+
 	return items.join(",");
 }