diff --git a/ChangeLog.md b/ChangeLog.md
index d1538ca..5a519ef 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -20,6 +20,8 @@ Generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).
 
 - Fix _send_packet()/_send_ack(): replace misleading `pass` with explicit comment explaining PacketTrack polling contract; restructure condition to `if not (scheduler and scheduler.is_alive()):` [`2842851`](https://github.com/craigerl/aprsd/commit/2842851)
 
+- Fix RejectPacket.__post__init__ typo — rename to __post_init__ so the dataclass lifecycle hook is actually called [`f75ed8a`](https://github.com/craigerl/aprsd/commit/f75ed8a)
+
 - Add reset() to @singleton decorator; update tests to use ClassName.reset() instead of ClassName.instance = None [`ef19aaa`](https://github.com/craigerl/aprsd/commit/ef19aaa)
 
 - Fix PacketTrack.keys/items/values — return list snapshots instead of live dict views outside the lock [`088436e`](https://github.com/craigerl/aprsd/commit/088436e)
diff --git a/aprsd/packets/core.py b/aprsd/packets/core.py
index f7cda4c..19e2a9c 100644
--- a/aprsd/packets/core.py
+++ b/aprsd/packets/core.py
@@ -229,7 +229,7 @@ class RejectPacket(Packet):
     _type: str = field(default='RejectPacket', hash=False)
     response: Optional[str] = field(default=None)
 
-    def __post__init__(self):
+    def __post_init__(self):
         if self.response:
             LOG.warning('Response set!')
 
diff --git a/tests/packets/test_packet.py b/tests/packets/test_packet.py
index cf7df68..c188154 100644
--- a/tests/packets/test_packet.py
+++ b/tests/packets/test_packet.py
@@ -125,3 +125,37 @@ class TestFactory(unittest.TestCase):
                 allowlist,
                 f'{cls.__name__} is in TYPE_LOOKUP but missing from the allowlist',
             )
+
+
+class TestRejectPacket(unittest.TestCase):
+    """Tests for RejectPacket dataclass lifecycle."""
+
+    def test_post_init_called_with_response(self):
+        """RejectPacket.__post_init__ must be called by the dataclass machinery.
+
+        The method was previously named __post__init__ (double underscores) which
+        is not a recognised dataclass lifecycle hook, so it was silently ignored.
+        """
+        import logging
+
+        with self.assertLogs(level=logging.WARNING) as cm:
+            packets.RejectPacket(
+                from_call=fake.FAKE_FROM_CALLSIGN,
+                to_call=fake.FAKE_TO_CALLSIGN,
+                response='REJ',
+            )
+        # The warning should have been emitted via __post_init__
+        self.assertTrue(
+            any('Response set!' in msg for msg in cm.output),
+            f'Expected "Response set!" warning; got: {cm.output}',
+        )
+
+    def test_post_init_called_without_response(self):
+        """RejectPacket.__post_init__ must not emit a warning when response is None."""
+        import logging
+
+        with self.assertNoLogs(level=logging.WARNING):
+            packets.RejectPacket(
+                from_call=fake.FAKE_FROM_CALLSIGN,
+                to_call=fake.FAKE_TO_CALLSIGN,
+            )