diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5bb27a80..9aa5bb7e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ All notable changes to this project will be documented in this file.
 ### Bug Fixes
 - Increase the allowable length of Matrix room alias to 100 (#320)
 - Make sure Check.last_ping and Ping.created timestamps match exactly
+- Don't trigger "down" notifications when changing schedule interactively in web UI
 
 
 ## v1.12.0 - 2020-01-02
diff --git a/hc/front/tests/test_update_timeout.py b/hc/front/tests/test_update_timeout.py
index 0b82909a..2404251e 100644
--- a/hc/front/tests/test_update_timeout.py
+++ b/hc/front/tests/test_update_timeout.py
@@ -31,7 +31,7 @@ class UpdateTimeoutTestCase(BaseTestCase):
         expected_aa = self.check.last_ping + td(seconds=3600 + 60)
         self.assertEqual(self.check.alert_after, expected_aa)
 
-    def test_it_does_not_update_status(self):
+    def test_it_does_not_update_status_to_up(self):
         self.check.last_ping = timezone.now() - td(days=2)
         self.check.status = "down"
         self.check.save()
@@ -45,6 +45,22 @@ class UpdateTimeoutTestCase(BaseTestCase):
         self.check.refresh_from_db()
         self.assertEqual(self.check.status, "down")
 
+    def test_it_updates_status_to_down(self):
+        self.check.last_ping = timezone.now() - td(hours=1)
+        self.check.status = "up"
+        self.check.alert_after = self.check.going_down_after()
+        self.check.save()
+
+        # 1 + 1 minute:
+        payload = {"kind": "simple", "timeout": 60, "grace": 60}
+
+        self.client.login(username="alice@example.org", password="password")
+        self.client.post(self.url, data=payload)
+
+        self.check.refresh_from_db()
+        self.assertEqual(self.check.status, "down")
+        self.assertIsNone(self.check.alert_after)
+
     def test_it_saves_cron_expression(self):
         payload = {"kind": "cron", "schedule": "5 * * * *", "tz": "UTC", "grace": 60}
 
diff --git a/hc/front/views.py b/hc/front/views.py
index ca7bc55c..926c4c01 100644
--- a/hc/front/views.py
+++ b/hc/front/views.py
@@ -377,6 +377,15 @@ def update_timeout(request, code):
         check.grace = td(minutes=form.cleaned_data["grace"])
 
     check.alert_after = check.going_down_after()
+    if check.status == "up" and check.alert_after < timezone.now():
+        # Checks can flip from "up" to "down" state as a result of changing check's
+        # schedule.  We don't want to send notifications when changing schedule
+        # interactively in the web UI. So we update the `alert_after` and `status`
+        # fields here the same way as `sendalerts` would do, but without sending
+        # an actual alert:
+        check.alert_after = None
+        check.status = "down"
+
     check.save()
 
     if "/details/" in request.META.get("HTTP_REFERER", ""):