diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py
index 0be977299..d7bcad8a8 100644
--- a/synapse/metrics/__init__.py
+++ b/synapse/metrics/__init__.py
@@ -158,18 +158,40 @@ def runUntilCurrentTimer(func):
 
     @functools.wraps(func)
     def f(*args, **kwargs):
-        pending_calls = len(reactor.getDelayedCalls())
+        now = reactor.seconds()
+        num_pending = 0
+
+        # _newTimedCalls is one long list of *all* pending calls. Below loop
+        # is based off of impl of reactor.runUntilCurrent
+        for delayed_call in reactor._newTimedCalls:
+            if delayed_call.time > now:
+                break
+
+            if delayed_call.delayed_time > 0:
+                continue
+
+            num_pending += 1
+
+        num_pending += len(reactor.threadCallQueue)
+
         start = time.time() * 1000
         ret = func(*args, **kwargs)
         end = time.time() * 1000
         tick_time.inc_by(end - start)
-        pending_calls_metric.inc_by(pending_calls)
+        pending_calls_metric.inc_by(num_pending)
         return ret
 
     return f
 
 
-if hasattr(reactor, "runUntilCurrent"):
+try:
+    # Ensure the reactor has all the attributes we expect
+    reactor.runUntilCurrent
+    reactor._newTimedCalls
+    reactor.threadCallQueue
+
     # runUntilCurrent is called when we have pending calls. It is called once
     # per iteratation after fd polling.
     reactor.runUntilCurrent = runUntilCurrentTimer(reactor.runUntilCurrent)
+except AttributeError:
+    pass