diff --git a/open_pcc_metric/metric.py b/open_pcc_metric/metric.py
index d1b5aa1..1453110 100644
--- a/open_pcc_metric/metric.py
+++ b/open_pcc_metric/metric.py
@@ -474,7 +474,7 @@ def __init__(
     def _key(self) -> str:
         if hasattr(self.metrics[0], "point_to_plane"):
             return "{label}({p2plane})(symmetric)".format(
-                label=metrics[0].label,
+                label=self.metrics[0].label,
                 p2plane="p2plane" if self.metrics[0].point_to_plane else "p2point",
             )
         return self.label