diff --git a/newsfragments/159.bugfix.rst b/newsfragments/159.bugfix.rst
new file mode 100644
index 00000000..7e4339eb
--- /dev/null
+++ b/newsfragments/159.bugfix.rst
@@ -0,0 +1 @@
+Allow ``loop.call_later()`` to accept negative delays, matching asyncio's behavior by scheduling the callback immediately.
diff --git a/tests/conftest.py b/tests/conftest.py
index 40dcd0da..bbcde9cb 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -211,6 +211,17 @@ def skip(rel_id):
                         item.add_marker(pytest.mark.skip)
 
         if sys.version_info >= (3, 11):
+            # CPython's SSLProtocol test intentionally leaves the two transports
+            # created while checking the missing-server_hostname warning without
+            # cleanup callbacks.  pytest 9 reports their finalizer warnings as
+            # unraisable exceptions, even though the test itself passes.
+            mark(
+                pytest.mark.filterwarnings("ignore:.*_SSLProtocolTransport.__del__.*"),
+                "test_sslproto.py::SslProtoHandshakeTests::"
+                "test_check_hostname_requires_server_hostname",
+                may_be_absent=True,
+            )
+
             # This tries to use a mock ChildWatcher that does something unlikely.
             # We don't support it because we don't actually use the ChildWatcher
             # to manage subprocesses.
diff --git a/tests/test_misc.py b/tests/test_misc.py
index be83b047..521328df 100644
--- a/tests/test_misc.py
+++ b/tests/test_misc.py
@@ -168,6 +168,16 @@ async def cancel_sleep():
         await trio_asyncio.aio_as_trio(cancel_sleep, loop=loop)()
         assert owch == 0
 
+    @pytest.mark.trio
+    async def test_call_later_accepts_negative_delay(self, loop):
+        called = trio.Event()
+
+        def callback():
+            called.set()
+
+        loop.call_later(-1, callback)
+        await called.wait()
+
 
 @pytest.mark.trio
 async def test_wrong_context_manager_order():
diff --git a/trio_asyncio/_base.py b/trio_asyncio/_base.py
index 77b00099..e74f28b0 100644
--- a/trio_asyncio/_base.py
+++ b/trio_asyncio/_base.py
@@ -364,7 +364,6 @@ def call_later(self, delay, callback, *args, **context):
         :return: a handle which may be used to cancel the timer.
         """
         self._check_callback(callback, "call_later")
-        assert delay >= 0, delay
         h = asyncio.TimerHandle(delay + self.time(), callback, args, self, **context)
         self._queue_handle(h)
         return h