diff --git a/src/capport/stats.py b/src/capport/stats.py
index 0898916..55ba4cc 100644
--- a/src/capport/stats.py
+++ b/src/capport/stats.py
@@ -17,7 +17,7 @@ from . import cptypes
 class MetricPrinter:
     args: CliArguments
     now: int | None = None
-    _known_names: set[str] = dataclasses.field(default_factory=set, init=None)
+    _known_names: set[str] = dataclasses.field(default_factory=set, init=False)
     _now_str: str = dataclasses.field(init=False)
     _label_str: str = dataclasses.field(init=False)