diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1e363f17..5060cf61 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,8 +10,9 @@ All notable changes to this project will be documented in this file.
 ### Bug Fixes
 - The "render_docs" command checks if markdown and pygments is installed (#329)
 - The team size limit is applied to the n. of distinct users across all projects (#332)
-- Don't let SuspiciousOperation bubble up when validating channel ids in API
-- Security: check channel ownership when setting check's channels via API
+- API: don't let SuspiciousOperation bubble up when validating channel ids
+- API security: check channel ownership when setting check's channels
+- API: update check's "alert_after" field when changing schedule
 
 ## v1.13.0 - 2020-02-13
 
diff --git a/hc/api/tests/test_update_check.py b/hc/api/tests/test_update_check.py
index 24b6da63..f689f193 100644
--- a/hc/api/tests/test_update_check.py
+++ b/hc/api/tests/test_update_check.py
@@ -1,5 +1,7 @@
+from datetime import timedelta as td
 import uuid
 
+from django.utils.timezone import now
 from hc.api.models import Channel, Check
 from hc.test import BaseTestCase
 
@@ -14,6 +16,10 @@ class UpdateCheckTestCase(BaseTestCase):
         return self.client.post(url, data, content_type="application/json")
 
     def test_it_works(self):
+        self.check.last_ping = now()
+        self.check.status = "up"
+        self.check.save()
+
         r = self.post(
             self.check.code,
             {
@@ -34,7 +40,6 @@ class UpdateCheckTestCase(BaseTestCase):
         self.assertEqual(doc["name"], "Foo")
         self.assertEqual(doc["tags"], "bar,baz")
         self.assertEqual(doc["desc"], "My description")
-        self.assertEqual(doc["last_ping"], None)
         self.assertEqual(doc["n_pings"], 0)
 
         self.assertTrue("schedule" not in doc)
@@ -48,6 +53,10 @@ class UpdateCheckTestCase(BaseTestCase):
         self.assertEqual(self.check.timeout.total_seconds(), 3600)
         self.assertEqual(self.check.grace.total_seconds(), 60)
 
+        # alert_after should be updated too
+        expected_aa = self.check.last_ping + td(seconds=3600 + 60)
+        self.assertEqual(self.check.alert_after, expected_aa)
+
     def test_it_handles_options(self):
         r = self.client.options("/api/v1/checks/%s" % self.check.code)
         self.assertEqual(r.status_code, 204)
diff --git a/hc/api/views.py b/hc/api/views.py
index d7662443..abcb67a8 100644
--- a/hc/api/views.py
+++ b/hc/api/views.py
@@ -89,6 +89,7 @@ def _update(check, spec):
         if "tz" in spec:
             check.tz = spec["tz"]
 
+    check.alert_after = check.going_down_after()
     check.save()
 
     # This needs to be done after saving the check, because of