diff --git a/zerver/lib/actions.py b/zerver/lib/actions.py
index 2e7a037eef..929a2311ad 100644
--- a/zerver/lib/actions.py
+++ b/zerver/lib/actions.py
@@ -865,9 +865,6 @@ def get_recipient_info(recipient, sender_id):
 
 def get_service_bot_events(sender, service_bot_tuples, mentioned_user_ids, recipient_type):
     # type: (UserProfile, List[Tuple[int, int]], Set[int], int) -> Dict[str, List[Dict[str, Any]]]
-    # TODO: Right now, service bots need to be subscribed to a stream in order to
-    # receive messages when mentioned; we will want to change that structure.
-    # Prepare to collect service queue events triggered by the message.
 
     event_dict = defaultdict(list)  # type: Dict[str, List[Dict[str, Any]]]
 
@@ -876,6 +873,27 @@ def get_service_bot_events(sender, service_bot_tuples, mentioned_user_ids, recip
     if sender.is_bot:
         return event_dict
 
+    if recipient_type == Recipient.STREAM:
+        known_ids = {user_profile_id for user_profile_id, bot_type in service_bot_tuples}
+        unknown_ids = mentioned_user_ids - known_ids
+        if unknown_ids:
+            '''
+            If we mention a service bot in a stream message, we should notify
+            them.  If the bot also happens to be subscribed to the stream, then
+            they would have already been in `service_bot_tuples`, but if
+            they are not subscribed to the stream, we need to go find them
+            in the follow up query below.  Also, it's important to filter
+            for service bots only.
+            '''
+            query = UserProfile.objects.filter(
+                id__in=unknown_ids,
+                is_active=True,
+                is_bot=True,
+                bot_type__in=UserProfile.SERVICE_BOT_TYPES,
+            ).values('id', 'bot_type')
+            tups = [(row['id'], row['bot_type']) for row in query]
+            service_bot_tuples += tups
+
     for user_profile_id, bot_type in service_bot_tuples:
         if bot_type == UserProfile.OUTGOING_WEBHOOK_BOT:
             queue_name = 'outgoing_webhooks'
diff --git a/zerver/tests/test_service_bot_system.py b/zerver/tests/test_service_bot_system.py
index b129c11b6b..e2e5c6a9b8 100644
--- a/zerver/tests/test_service_bot_system.py
+++ b/zerver/tests/test_service_bot_system.py
@@ -84,6 +84,42 @@ class TestServiceBotBasics(ZulipTestCase):
 
         self.assertEqual(event_dict, expected)
 
+    def test_service_events_for_unsubscribed_stream_mentions(self):
+        # type: () -> None
+        sender = self.example_user('hamlet')
+        assert(not sender.is_bot)
+
+        outgoing_bot = self._get_outgoing_bot()
+
+        '''
+        If an outgoing bot is mentioned on a stream message, we will
+        create an event for it even if it is not subscribed to the
+        stream and not part of our original `service_bot_tuples`.
+
+        Note that we add Cordelia as a red herring value that the
+        code should ignore, since she is not a bot.
+        '''
+
+        cordelia = self.example_user('cordelia')
+
+        event_dict = get_service_bot_events(
+            sender=sender,
+            service_bot_tuples=[],
+            mentioned_user_ids={
+                outgoing_bot.id,
+                cordelia.id,  # should be excluded, not a service bot
+            },
+            recipient_type=Recipient.STREAM,
+        )
+
+        expected = dict(
+            outgoing_webhooks=[
+                dict(trigger='mention', user_profile_id=outgoing_bot.id),
+            ],
+        )
+
+        self.assertEqual(event_dict, expected)
+
 class TestServiceBotEventTriggers(ZulipTestCase):
 
     def setUp(self):