diff --git a/artiq/master/scheduler.py b/artiq/master/scheduler.py
index d849880fe..1a18c0720 100644
--- a/artiq/master/scheduler.py
+++ b/artiq/master/scheduler.py
@@ -332,10 +332,10 @@ class Pipeline:
         self._run = RunStage(self.pool, deleter.delete)
         self._analyze = AnalyzeStage(self.pool, deleter.delete)
 
-    def start(self, loop=None):
-        self._prepare.start(loop)
-        self._run.start(loop)
-        self._analyze.start(loop)
+    def start(self, *, loop=None):
+        self._prepare.start(loop=loop)
+        self._run.start(loop=loop)
+        self._analyze.start(loop=loop)
 
     async def stop(self):
         # NB: restart of a stopped pipeline is not supported
@@ -410,9 +410,9 @@ class Scheduler:
         self._deleter = Deleter(self._pipelines)
         self._log_submissions = log_submissions
 
-    def start(self, loop=None):
+    def start(self, *, loop=None):
         self._loop = loop
-        self._deleter.start(self._loop)
+        self._deleter.start(loop=self._loop)
 
     async def stop(self):
         # NB: restart of a stopped scheduler is not supported
diff --git a/artiq/test/test_scheduler.py b/artiq/test/test_scheduler.py
index 5ed6cc01a..9726190ed 100644
--- a/artiq/test/test_scheduler.py
+++ b/artiq/test/test_scheduler.py
@@ -104,7 +104,7 @@ class SchedulerCase(unittest.TestCase):
                 done.set()
         scheduler.notifier.publish = notify
 
-        scheduler.start(loop)
+        scheduler.start(loop=loop)
 
         # Verify that a timed experiment far in the future does not
         # get run, even if it has high priority.
@@ -269,7 +269,7 @@ class SchedulerCase(unittest.TestCase):
                 done.set()
         scheduler.notifier.publish = notify
 
-        scheduler.start(loop)
+        scheduler.start(loop=loop)
 
         scheduler.submit("main", expid_bg, low_priority)
         scheduler.submit("main", expid_empty, high_priority, late)
@@ -328,7 +328,7 @@ class SchedulerCase(unittest.TestCase):
                     empty_completed.set()
         scheduler.notifier.publish = notify
 
-        scheduler.start(loop)
+        scheduler.start(loop=loop)
         scheduler.submit("main", expid_bg, -99, None, False)
         loop.run_until_complete(background_running.wait())
         self.assertFalse(scheduler.check_pause(0))
@@ -379,7 +379,7 @@ class SchedulerCase(unittest.TestCase):
                 empty_ready.set()
         scheduler.notifier.publish = notify
 
-        scheduler.start(loop)
+        scheduler.start(loop=loop)
         scheduler.submit("main", expid_bg, -99, None, False)
         loop.run_until_complete(background_running.wait())
 
@@ -417,7 +417,7 @@ class SchedulerCase(unittest.TestCase):
                     done.set()
         scheduler.notifier.publish = notify
 
-        scheduler.start(loop)
+        scheduler.start(loop=loop)
         scheduler.submit("main", expid, 0, None, False)
         loop.run_until_complete(first_preparing.wait())
         scheduler.submit("main", expid, 1, None, True)