diff --git a/changelog.d/10107.bugfix b/changelog.d/10107.bugfix
new file mode 100644
index 000000000..80030efab
--- /dev/null
+++ b/changelog.d/10107.bugfix
@@ -0,0 +1 @@
+Fixed a bug that could cause Synapse to stop notifying application services. Contributed by Willem Mulder.
diff --git a/synapse/handlers/appservice.py b/synapse/handlers/appservice.py
index 177310f0b..862638cc4 100644
--- a/synapse/handlers/appservice.py
+++ b/synapse/handlers/appservice.py
@@ -87,7 +87,8 @@ class ApplicationServicesHandler:
             self.is_processing = True
             try:
                 limit = 100
-                while True:
+                upper_bound = -1
+                while upper_bound < self.current_max:
                     (
                         upper_bound,
                         events,
@@ -95,9 +96,6 @@ class ApplicationServicesHandler:
                         self.current_max, limit
                     )
 
-                    if not events:
-                        break
-
                     events_by_room = {}  # type: Dict[str, List[EventBase]]
                     for event in events:
                         events_by_room.setdefault(event.room_id, []).append(event)
@@ -153,9 +151,6 @@ class ApplicationServicesHandler:
 
                     await self.store.set_appservice_last_pos(upper_bound)
 
-                    now = self.clock.time_msec()
-                    ts = await self.store.get_received_ts(events[-1].event_id)
-
                     synapse.metrics.event_processing_positions.labels(
                         "appservice_sender"
                     ).set(upper_bound)
@@ -168,12 +163,16 @@ class ApplicationServicesHandler:
 
                     event_processing_loop_counter.labels("appservice_sender").inc()
 
-                    synapse.metrics.event_processing_lag.labels(
-                        "appservice_sender"
-                    ).set(now - ts)
-                    synapse.metrics.event_processing_last_ts.labels(
-                        "appservice_sender"
-                    ).set(ts)
+                    if events:
+                        now = self.clock.time_msec()
+                        ts = await self.store.get_received_ts(events[-1].event_id)
+
+                        synapse.metrics.event_processing_lag.labels(
+                            "appservice_sender"
+                        ).set(now - ts)
+                        synapse.metrics.event_processing_last_ts.labels(
+                            "appservice_sender"
+                        ).set(ts)
             finally:
                 self.is_processing = False
 
diff --git a/tests/handlers/test_appservice.py b/tests/handlers/test_appservice.py
index b037b12a0..5d6cc2885 100644
--- a/tests/handlers/test_appservice.py
+++ b/tests/handlers/test_appservice.py
@@ -57,10 +57,10 @@ class AppServiceHandlerTestCase(unittest.TestCase):
             sender="@someone:anywhere", type="m.room.message", room_id="!foo:bar"
         )
         self.mock_store.get_new_events_for_appservice.side_effect = [
-            make_awaitable((0, [event])),
             make_awaitable((0, [])),
+            make_awaitable((1, [event])),
         ]
-        self.handler.notify_interested_services(RoomStreamToken(None, 0))
+        self.handler.notify_interested_services(RoomStreamToken(None, 1))
 
         self.mock_scheduler.submit_event_for_as.assert_called_once_with(
             interested_service, event
@@ -77,7 +77,6 @@ class AppServiceHandlerTestCase(unittest.TestCase):
         self.mock_as_api.query_user.return_value = make_awaitable(True)
         self.mock_store.get_new_events_for_appservice.side_effect = [
             make_awaitable((0, [event])),
-            make_awaitable((0, [])),
         ]
 
         self.handler.notify_interested_services(RoomStreamToken(None, 0))
@@ -95,7 +94,6 @@ class AppServiceHandlerTestCase(unittest.TestCase):
         self.mock_as_api.query_user.return_value = make_awaitable(True)
         self.mock_store.get_new_events_for_appservice.side_effect = [
             make_awaitable((0, [event])),
-            make_awaitable((0, [])),
         ]
 
         self.handler.notify_interested_services(RoomStreamToken(None, 0))