1 files changed, 10 insertions, 2 deletions
diff --git a/synapse/util/metrics.py b/synapse/util/metrics.py
index 1e784b3f1f..98ee49af6e 100644
--- a/synapse/util/metrics.py
+++ b/synapse/util/metrics.py
@@ -56,14 +56,22 @@ block_db_sched_duration = Counter(
     "synapse_util_metrics_block_db_sched_duration_seconds", "", ["block_name"]
 )
 
+
+# This is dynamically created in InFlightGauge.__init__.
+class _InFlightMetric(Protocol):
+    real_time_max: float
+    real_time_sum: float
+
+
 # Tracks the number of blocks currently active
-in_flight = InFlightGauge(
+in_flight: InFlightGauge[_InFlightMetric] = InFlightGauge(
     "synapse_util_metrics_block_in_flight",
     "",
     labels=["block_name"],
     sub_metrics=["real_time_max", "real_time_sum"],
 )
 
+
 T = TypeVar("T", bound=Callable[..., Any])
 
 
@@ -180,7 +188,7 @@ class Measure:
         """
         return self._logging_context.get_resource_usage()
 
-    def _update_in_flight(self, metrics) -> None:
+    def _update_in_flight(self, metrics: _InFlightMetric) -> None:
         """Gets called when processing in flight metrics"""
         assert self.start is not None
         duration = self.clock.time() - self.start