diff --git a/changelog.d/1334.downstream.rst b/changelog.d/1334.downstream.rst
new file mode 100644
index 00000000..ba2e2505
--- /dev/null
+++ b/changelog.d/1334.downstream.rst
@@ -0,0 +1 @@
+Avoided a ``PytestAssertRewriteWarning`` in the test suite when pytest-asyncio is already imported, such as when tests are run against a system-installed copy on Guix or FreeBSD.
diff --git a/tests/markers/test_class_scope.py b/tests/markers/test_class_scope.py
index 28f7187c..4ee6951f 100644
--- a/tests/markers/test_class_scope.py
+++ b/tests/markers/test_class_scope.py
@@ -274,5 +274,5 @@ class TestClass:
                 async def test_anything(self):
                     pass
             """))
-    result = pytester.runpytest("--asyncio-mode=strict")
+    result = pytester.runpytest("--asyncio-mode=strict", "--assert=plain")
     result.assert_outcomes(warnings=0, passed=1)
diff --git a/tests/markers/test_function_scope.py b/tests/markers/test_function_scope.py
index 180d5c71..1e797895 100644
--- a/tests/markers/test_function_scope.py
+++ b/tests/markers/test_function_scope.py
@@ -72,7 +72,9 @@ def test_warns_when_scope_argument_is_present(pytester: Pytester):
             async def test_warns():
                 ...
             """))
-    result = pytester.runpytest("--asyncio-mode=strict", "-W", "default")
+    result = pytester.runpytest(
+        "--asyncio-mode=strict", "-W", "default", "--assert=plain"
+    )
     result.assert_outcomes(passed=1, warnings=1)
     result.stdout.fnmatch_lines("*DeprecationWarning*")
 
diff --git a/tests/markers/test_module_scope.py b/tests/markers/test_module_scope.py
index a2662812..c1e6ff99 100644
--- a/tests/markers/test_module_scope.py
+++ b/tests/markers/test_module_scope.py
@@ -281,5 +281,5 @@ def test_standalone_test_does_not_trigger_warning_about_no_current_event_loop_be
             async def test_anything():
                 pass
             """))
-    result = pytester.runpytest("--asyncio-mode=strict")
+    result = pytester.runpytest("--asyncio-mode=strict", "--assert=plain")
     result.assert_outcomes(warnings=0, passed=1)
diff --git a/tests/markers/test_session_scope.py b/tests/markers/test_session_scope.py
index 24566c5e..6cd85a55 100644
--- a/tests/markers/test_session_scope.py
+++ b/tests/markers/test_session_scope.py
@@ -392,5 +392,5 @@ def test_standalone_test_does_not_trigger_warning_about_no_current_event_loop_be
             async def test_anything():
                 pass
             """))
-    result = pytester.runpytest("--asyncio-mode=strict")
+    result = pytester.runpytest("--asyncio-mode=strict", "--assert=plain")
     result.assert_outcomes(warnings=0, passed=1)
diff --git a/tests/test_event_loop_fixture.py b/tests/test_event_loop_fixture.py
index 8902511b..08355f04 100644
--- a/tests/test_event_loop_fixture.py
+++ b/tests/test_event_loop_fixture.py
@@ -13,8 +13,6 @@ def test_event_loop_fixture_handles_unclosed_async_gen(
             import asyncio
             import pytest
 
-            pytest_plugins = 'pytest_asyncio'
-
             @pytest.mark.asyncio
             async def test_something():
                 async def generator_fn():
@@ -67,8 +65,6 @@ def test_event_loop_fixture_asyncgen_error(
             import asyncio
             import pytest
 
-            pytest_plugins = 'pytest_asyncio'
-
             @pytest.mark.asyncio
             async def test_something():
                 # mock shutdown_asyncgen failure