diff --git a/synapse/metrics/_gc.py b/synapse/metrics/_gc.py
index b7d47ce3e7..296e0a59cb 100644
--- a/synapse/metrics/_gc.py
+++ b/synapse/metrics/_gc.py
@@ -129,7 +129,7 @@ def install_gc_manager() -> None:
                 gc_unreachable.labels(i).set(unreachable)
 
     gc_task = task.LoopingCall(_maybe_gc)
-    gc_task.start(0.1)
+    gc_task.start(0.1) # type: ignore[unused-awaitable]
 
 
 #