diff --git a/CHANGES/3450.bugfix b/CHANGES/3450.bugfix
new file mode 100644
index 00000000000..6b82b4c0481
--- /dev/null
+++ b/CHANGES/3450.bugfix
@@ -0,0 +1 @@
+Started using `MultiLoopChildWatcher` when it's available under POSIX while setting up the test I/O loop.
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 502efb67a20..b9361827b66 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -241,6 +241,7 @@ Pawel Miech
 Pepe Osca
 Philipp A.
 Pieter van Beek
+Qiao Han
 Rafael Viotti
 Raphael Bialon
 Raúl Cumplido
diff --git a/aiohttp/test_utils.py b/aiohttp/test_utils.py
index e8ebb6d4ed0..06155bae19f 100644
--- a/aiohttp/test_utils.py
+++ b/aiohttp/test_utils.py
@@ -490,7 +490,16 @@ def setup_test_loop(
     asyncio.set_event_loop(loop)
     if sys.platform != "win32" and not skip_watcher:
         policy = asyncio.get_event_loop_policy()
-        watcher = asyncio.SafeChildWatcher()
+        watcher: asyncio.AbstractChildWatcher
+        try:  # Python >= 3.8
+            # Refs:
+            # * https://github.com/pytest-dev/pytest-xdist/issues/620
+            # * https://stackoverflow.com/a/58614689/595220
+            # * https://bugs.python.org/issue35621
+            # * https://github.com/python/cpython/pull/14344
+            watcher = asyncio.MultiLoopChildWatcher()
+        except AttributeError:  # Python < 3.8
+            watcher = asyncio.SafeChildWatcher()
         watcher.attach_loop(loop)
         with contextlib.suppress(NotImplementedError):
             policy.set_child_watcher(watcher)