diff --git a/declearn/metrics/_wrapper.py b/declearn/metrics/_wrapper.py
index fe9e469357446c8d3a0a61000d7b949d26873b69..e56746466479a2c76e2c00dbf845c5ac9fbc5bf4 100644
--- a/declearn/metrics/_wrapper.py
+++ b/declearn/metrics/_wrapper.py
@@ -129,8 +129,8 @@ class MetricSet:
             metrics = cls(metrics)
         if not isinstance(metrics, cls):
             raise TypeError(
-                "'metrics' should be a `{cls.name}`, a valid list of Metric "
-                "instances and/or specs to wrap into one, or None."
+                f"'metrics' should be a `{cls.__name__}`, a valid list of "
+                "Metric instances and/or specs to wrap into one, or None."
             )
         return metrics