diff --git a/CHANGES/101.contrib.rst b/CHANGES/101.contrib.rst
new file mode 100644
index 0000000..6dd107f
--- /dev/null
+++ b/CHANGES/101.contrib.rst
@@ -0,0 +1,3 @@
+Added regression tests pinning the ``mdns_timeout`` seconds-to-milliseconds
+conversion that ``AsyncMDNSResolver`` forwards to ``zeroconf``'s
+``async_request`` -- by :user:`aiolibsbot`.
diff --git a/tests/test_mdns_timeout_conversion.py b/tests/test_mdns_timeout_conversion.py
new file mode 100644
index 0000000..f779f04
--- /dev/null
+++ b/tests/test_mdns_timeout_conversion.py
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+"""Lock the ``mdns_timeout`` seconds-to-milliseconds conversion.
+
+The public ``mdns_timeout`` constructor argument is documented in seconds, but
+``zeroconf``'s ``async_request`` expects a timeout in **milliseconds**. The
+resolver bridges the two by multiplying by 1000 before issuing the network
+query. None of the existing tests assert the value handed to ``async_request``
+(they stub it with ``return_value=True`` regardless of its arguments), so a
+refactor dropping the ``* 1000`` would silently turn a 5-second timeout into a
+5-millisecond one and the whole suite would still pass. These tests pin that
+conversion against the observable call.
+"""
+
+import socket
+from collections.abc import AsyncGenerator
+from ipaddress import IPv4Address
+from typing import Any
+from unittest.mock import patch
+
+import pytest
+import pytest_asyncio
+
+from aiohttp_asyncmdnsresolver._impl import (
+    _FAMILY_TO_RESOLVER_CLASS,
+    DEFAULT_TIMEOUT,
+    AddressResolverIPv4,
+)
+from aiohttp_asyncmdnsresolver.api import AsyncMDNSResolver
+
+
+class IPv4HostResolver(AddressResolverIPv4):
+    """Patchable subclass so ``async_request`` can be intercepted."""
+
+
+@pytest.fixture(autouse=True)
+def make_resolvers_patchable() -> Any:
+    """Route AF_INET lookups through the patchable subclass."""
+    with patch.dict(_FAMILY_TO_RESOLVER_CLASS, {socket.AF_INET: IPv4HostResolver}):
+        yield
+
+
+@pytest_asyncio.fixture
+async def make_resolver() -> AsyncGenerator[Any]:
+    """Build resolvers via the public constructor and close them on teardown."""
+    resolvers: list[AsyncMDNSResolver] = []
+
+    def _factory(**kwargs: Any) -> AsyncMDNSResolver:
+        resolver = AsyncMDNSResolver(**kwargs)
+        resolvers.append(resolver)
+        return resolver
+
+    yield _factory
+    for resolver in resolvers:
+        await resolver.close()
+
+
+async def _resolve_and_capture_timeout(
+    resolver: AsyncMDNSResolver,
+) -> tuple[Any, float]:
+    """Resolve a cache-miss ``.local`` name and return the ``async_request`` args."""
+    with (
+        patch.object(IPv4HostResolver, "load_from_cache", return_value=False),
+        patch.object(
+            IPv4HostResolver, "async_request", return_value=True
+        ) as async_request,
+        patch.object(
+            IPv4HostResolver,
+            "ip_addresses_by_version",
+            return_value=[IPv4Address("127.0.0.1")],
+        ),
+    ):
+        result = await resolver.resolve("printer.local", family=socket.AF_INET)
+
+    assert result[0]["host"] == "127.0.0.1"
+    async_request.assert_called_once()
+    zeroconf_arg, timeout_arg = async_request.call_args.args
+    return zeroconf_arg, timeout_arg
+
+
+@pytest.mark.asyncio
+async def test_mdns_timeout_seconds_converted_to_milliseconds(
+    make_resolver: Any,
+) -> None:
+    """A non-default ``mdns_timeout`` in seconds reaches zeroconf in ms."""
+    resolver = make_resolver(mdns_timeout=2.5)
+
+    zeroconf_arg, timeout_arg = await _resolve_and_capture_timeout(resolver)
+
+    assert timeout_arg == 2500.0
+    # The query is issued through the resolver's own zeroconf instance.
+    assert zeroconf_arg is resolver._aiozc.zeroconf
+
+
+@pytest.mark.asyncio
+async def test_default_mdns_timeout_passed_in_milliseconds(
+    make_resolver: Any,
+) -> None:
+    """The default ``mdns_timeout`` (seconds) is forwarded as milliseconds."""
+    resolver = make_resolver()
+
+    _, timeout_arg = await _resolve_and_capture_timeout(resolver)
+
+    assert timeout_arg == DEFAULT_TIMEOUT * 1000
+    assert timeout_arg == 5000.0