diff --git a/src/textual_webterm/local_server.py b/src/textual_webterm/local_server.py
index 96db4a5..859983f 100644
--- a/src/textual_webterm/local_server.py
+++ b/src/textual_webterm/local_server.py
@@ -346,9 +346,9 @@ class LocalServer:
         if msg_type == "stdin":
             await self._handle_stdin(envelope, route_key, ws)
         elif msg_type == "resize":
-            if not session_created and await self._handle_resize(envelope, route_key, ws):
-                session_created = True
-            elif session_created:
+            if not session_created:
+                session_created = await self._handle_resize(envelope, route_key, ws)
+            else:
                 await self._handle_resize(envelope, route_key, ws)
         elif msg_type == "ping":
             await self._handle_ping(envelope, route_key, ws)
diff --git a/src/textual_webterm/poller.py b/src/textual_webterm/poller.py
index 8462c95..80e4529 100644
--- a/src/textual_webterm/poller.py
+++ b/src/textual_webterm/poller.py
@@ -62,7 +62,17 @@ class Poller(Thread):
             self._write_queues[file_descriptor] = deque()
         new_write = Write(data)
         self._write_queues[file_descriptor].append(new_write)
-        self._selector.modify(file_descriptor, selectors.EVENT_READ | selectors.EVENT_WRITE)
+        try:
+
+            self._selector.modify(file_descriptor, selectors.EVENT_READ | selectors.EVENT_WRITE)
+
+        except KeyError:
+
+            # File descriptor removed concurrently
+
+            new_write.done_event.set()
+
+            return
         await new_write.done_event.wait()
 
     def set_loop(self, loop: asyncio.AbstractEventLoop) -> None:
diff --git a/src/textual_webterm/terminal_session.py b/src/textual_webterm/terminal_session.py
index 739b7df..bd694a6 100644
--- a/src/textual_webterm/terminal_session.py
+++ b/src/textual_webterm/terminal_session.py
@@ -253,9 +253,13 @@ class TerminalSession(Session):
                 os.close(fd)
 
     async def send_bytes(self, data: bytes) -> bool:
-        if self.master_fd is None:
+        fd = self.master_fd
+        if fd is None:
+            return False
+        try:
+            await self.poller.write(fd, data)
+        except (KeyError, OSError):
             return False
-        await self.poller.write(self.master_fd, data)
         return True
 
     async def send_meta(self, data: Meta) -> bool:
diff --git a/tests/test_local_server_unit.py b/tests/test_local_server_unit.py
index c2ff8e6..53d8d0a 100644
--- a/tests/test_local_server_unit.py
+++ b/tests/test_local_server_unit.py
@@ -679,6 +679,19 @@ class TestLocalServerMoreCoverage:
         session.send_bytes.assert_awaited_once_with(b"")
 
     @pytest.mark.asyncio
+    @pytest.mark.asyncio
+    async def test_dispatch_ws_message_resize_existing_session_flag_false(self, server_with_no_apps, monkeypatch):
+        session = MagicMock()
+        session.set_terminal_size = AsyncMock()
+        monkeypatch.setattr(server_with_no_apps.session_manager, "get_session_by_route_key", lambda _rk: session)
+
+        ws = MagicMock()
+        created = await server_with_no_apps._dispatch_ws_message(
+            ["resize", {"width": 100, "height": 50}], "rk", ws, False
+        )
+        assert created is False
+        session.set_terminal_size.assert_awaited_once_with(100, 50)
+
     async def test_dispatch_ws_message_resize_updates_existing_session(self, server_with_no_apps, monkeypatch):
         session = MagicMock()
         session.set_terminal_size = AsyncMock()
diff --git a/tests/test_poller.py b/tests/test_poller.py
index 65a29bb..1c5fd67 100644
--- a/tests/test_poller.py
+++ b/tests/test_poller.py
@@ -71,6 +71,17 @@ class TestPoller:
             # Should not raise
             poller.remove_file(999)
 
+    @pytest.mark.asyncio
+    async def test_write_handles_removed_fd(self):
+        poller = Poller()
+        poller._loop = asyncio.get_event_loop()
+
+        with patch.object(poller._selector, "register"):
+            poller.add_file(42)
+
+        with patch.object(poller._selector, "modify", side_effect=KeyError()):
+            await poller.write(42, b"test")
+
     @pytest.mark.asyncio
     async def test_write_creates_queue(self):
         """Test that write creates a write queue if needed."""
diff --git a/tests/test_terminal_session.py b/tests/test_terminal_session.py
index 938f01d..f827b1e 100644
--- a/tests/test_terminal_session.py
+++ b/tests/test_terminal_session.py
@@ -288,6 +288,18 @@ class TestTerminalSession:
 
         mock_exit.assert_called_once_with(1)
 
+    @pytest.mark.asyncio
+    async def test_send_bytes_handles_closed_fd(self):
+        from textual_webterm.terminal_session import TerminalSession
+
+        poller = MagicMock()
+        poller.write = AsyncMock(side_effect=KeyError)
+        session = TerminalSession(poller, "sid", "bash")
+        session.master_fd = 10
+
+        ok = await session.send_bytes(b"test")
+        assert ok is False
+
     @pytest.mark.asyncio
     async def test_run_reads_from_poller_and_closes(self):
         from textual_webterm.terminal_session import TerminalSession