diff --git a/prometheus_client/metrics.py b/prometheus_client/metrics.py
index 4c79c583..ed586967 100644
--- a/prometheus_client/metrics.py
+++ b/prometheus_client/metrics.py
@@ -122,9 +122,10 @@ def __init__(self: T,
 
         _validate_metric_name(self._name)
 
+        self._lock = Lock()
+
         if self._is_parent():
             # Prepare the fields needed for child metrics.
-            self._lock = Lock()
             self._metrics: Dict[Sequence[str], T] = {}
 
         if self._is_observable():