diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py
index b29cec3de..bdd7292a3 100644
--- a/synapse/metrics/__init__.py
+++ b/synapse/metrics/__init__.py
@@ -156,6 +156,10 @@ pending_calls_metric = reactor_metrics.register_distribution("pending_calls")
 gc_time = reactor_metrics.register_distribution("gc_time", labels=["gen"])
 gc_unreachable = reactor_metrics.register_counter("gc_unreachable", labels=["gen"])
 
+reactor_metrics.register_callback(
+    "gc_counts", lambda: {(i,): v for i, v in enumerate(gc.get_count())}, labels=["gen"]
+)
+
 
 def runUntilCurrentTimer(func):