diff --git a/tests/util/test_linearizer.py b/tests/util/test_linearizer.py
index 7510657b85..1aca5a2eb4 100644
--- a/tests/util/test_linearizer.py
+++ b/tests/util/test_linearizer.py
@@ -21,14 +21,14 @@
 
 from typing import Hashable, Protocol, Tuple
 
-from twisted.internet import defer, reactor
-from twisted.internet.base import ReactorBase
+from twisted.internet import defer
 from twisted.internet.defer import CancelledError, Deferred
 
 from synapse.logging.context import LoggingContext, current_context
 from synapse.util.async_helpers import Linearizer
 
 from tests import unittest
+from tests.server import get_clock
 
 
 class UnblockFunction(Protocol):
@@ -36,6 +36,9 @@ class UnblockFunction(Protocol):
 
 
 class LinearizerTestCase(unittest.TestCase):
+    def setUp(self) -> None:
+        self.reactor, self.clock = get_clock()
+
     def _start_task(
         self, linearizer: Linearizer, key: Hashable
     ) -> Tuple["Deferred[None]", "Deferred[None]", UnblockFunction]:
@@ -67,19 +70,13 @@ class LinearizerTestCase(unittest.TestCase):
             # The next task, if it exists, will acquire the lock and require a kick of
             # the reactor to advance.
             if pump_reactor:
-                self._pump()
+                self.reactor.pump([0.0])
 
         return d, acquired_d, unblock
 
-    def _pump(self) -> None:
-        """Pump the reactor to advance `Linearizer`s."""
-        assert isinstance(reactor, ReactorBase)
-        while reactor.getDelayedCalls():
-            reactor.runUntilCurrent()
-
     def test_linearizer(self) -> None:
         """Tests that a task is queued up behind an earlier task."""
-        linearizer = Linearizer()
+        linearizer = Linearizer(clock=self.clock)
 
         key = object()
 
@@ -100,7 +97,7 @@ class LinearizerTestCase(unittest.TestCase):
 
         Runs through the same scenario as `test_linearizer`.
         """
-        linearizer = Linearizer()
+        linearizer = Linearizer(clock=self.clock)
 
         key = object()
 
@@ -131,7 +128,7 @@ class LinearizerTestCase(unittest.TestCase):
 
         The stack should *not* explode when the slow thing completes.
         """
-        linearizer = Linearizer()
+        linearizer = Linearizer(clock=self.clock)
         key = ""
 
         async def func(i: int) -> None:
@@ -151,7 +148,7 @@ class LinearizerTestCase(unittest.TestCase):
 
     def test_multiple_entries(self) -> None:
         """Tests a `Linearizer` with a concurrency above 1."""
-        limiter = Linearizer(max_count=3)
+        limiter = Linearizer(clock=self.clock, max_count=3)
 
         key = object()
 
@@ -192,7 +189,7 @@ class LinearizerTestCase(unittest.TestCase):
 
     def test_cancellation(self) -> None:
         """Tests cancellation while waiting for a `Linearizer`."""
-        linearizer = Linearizer()
+        linearizer = Linearizer(clock=self.clock)
 
         key = object()
 
@@ -226,7 +223,7 @@ class LinearizerTestCase(unittest.TestCase):
 
     def test_cancellation_during_sleep(self) -> None:
         """Tests cancellation during the sleep just after waiting for a `Linearizer`."""
-        linearizer = Linearizer()
+        linearizer = Linearizer(clock=self.clock)
 
         key = object()
 
@@ -246,7 +243,7 @@ class LinearizerTestCase(unittest.TestCase):
         unblock1(pump_reactor=False)
         self.successResultOf(d1)
         d2.cancel()
-        self._pump()
+        self.reactor.pump([0.0])
 
         self.assertTrue(d2.called)
         self.failureResultOf(d2, CancelledError)