diff --git a/tests/test_memusage_integration.py b/tests/test_memusage_integration.py
index f3a0e0931..fc4921bad 100644
--- a/tests/test_memusage_integration.py
+++ b/tests/test_memusage_integration.py
@@ -8,7 +8,6 @@ from twisted.internet.defer import inlineCallbacks
 
 from scrapy import signals
 from scrapy.extensions.memusage import MemoryUsage
-from scrapy.settings import Settings
 from scrapy.spiders import Spider
 from scrapy.utils.test import get_crawler
 
@@ -18,17 +17,6 @@ pytestmark = pytest.mark.skipif(
     reason="MemoryUsage extension not available on Windows",
 )
 
-MiB = 1024 * 1024
-
-
-def _installed_reactor_path() -> str:
-    """Return the fully qualified path of the *already installed* Twisted reactor.
-    Local import avoids module-level reactor import (keeps Ruff happy)."""
-    from twisted.internet import reactor as _reactor  # local on purpose
-
-    cls = _reactor.__class__
-    return f"{cls.__module__}.{cls.__name__}"
-
 
 class _LoopSpider(Spider):
     name = "loop-data-spider"
@@ -50,21 +38,18 @@ class _LoopSpider(Spider):
 @inlineCallbacks
 def test_memusage_limit_closes_spider_with_reason_and_error_log(caplog, monkeypatch):
     url = "data:,"
-    settings = Settings(
-        {
-            "MEMUSAGE_ENABLED": True,
-            "MEMUSAGE_LIMIT_MB": 10,
-            "MEMUSAGE_CHECK_INTERVAL_SECONDS": 0.01,
-            "LOG_LEVEL": "INFO",
-        }
-    )
-    # Respect the reactor already installed by the test env/CI.
-    settings.set("TWISTED_REACTOR", _installed_reactor_path(), priority="cmdline")
+    settings = {
+        "MEMUSAGE_ENABLED": True,
+        "MEMUSAGE_LIMIT_MB": 10,
+        "MEMUSAGE_CHECK_INTERVAL_SECONDS": 0.01,
+        "LOG_LEVEL": "INFO",
+    }
 
+    MB = 1024 * 1024
     state = {"high": False}
 
     def fake_vsz(self):
-        return 250 * MiB if state["high"] else 5 * MiB
+        return 250 * MB if state["high"] else 5 * MB
 
     monkeypatch.setattr(MemoryUsage, "get_virtual_size", fake_vsz)
 
@@ -87,19 +72,16 @@ def test_memusage_limit_closes_spider_with_reason_and_error_log(caplog, monkeypa
 @inlineCallbacks
 def test_memusage_warning_logs_but_allows_normal_finish(caplog, monkeypatch):
     url = "data:,"
-    settings = Settings(
-        {
-            "MEMUSAGE_ENABLED": True,
-            "MEMUSAGE_WARNING_MB": 50,
-            "MEMUSAGE_LIMIT_MB": 0,  # no hard limit
-            "MEMUSAGE_CHECK_INTERVAL_SECONDS": 0.01,
-            "LOG_LEVEL": "INFO",
-        }
-    )
-    # Respect the reactor already installed by the test env/CI.
-    settings.set("TWISTED_REACTOR", _installed_reactor_path(), priority="cmdline")
+    settings = {
+        "MEMUSAGE_ENABLED": True,
+        "MEMUSAGE_WARNING_MB": 50,
+        "MEMUSAGE_LIMIT_MB": 0,  # no hard limit
+        "MEMUSAGE_CHECK_INTERVAL_SECONDS": 0.01,
+        "LOG_LEVEL": "INFO",
+    }
 
-    monkeypatch.setattr(MemoryUsage, "get_virtual_size", lambda self: 75 * MiB)
+    MB = 1024 * 1024
+    monkeypatch.setattr(MemoryUsage, "get_virtual_size", lambda self: 75 * MB)
 
     crawler = get_crawler(spidercls=_LoopSpider, settings_dict=settings)