diff --git a/cli/src/mpftp/rawpaste.py b/cli/src/mpftp/rawpaste.py
index dad524b..535a1ac 100644
--- a/cli/src/mpftp/rawpaste.py
+++ b/cli/src/mpftp/rawpaste.py
@@ -118,6 +118,10 @@ def __init__(
             self.use_raw_paste = True
             self.device_name = device
             self.mounted = False
+            # mpremote 1.29 reads is_pty when it waits for the board; its own
+            # __init__, skipped here, sets it from the device path.
+            is_pty = getattr(SerialTransport, "_is_pty_device", None)
+            self.is_pty = bool(is_pty(device)) if is_pty else False
             kwargs: dict[str, Any] = {
                 "baudrate": baudrate,
                 "timeout": timeout,
diff --git a/cli/tests/test_stray_output.py b/cli/tests/test_stray_output.py
index 83bc666..b9aa4d6 100644
--- a/cli/tests/test_stray_output.py
+++ b/cli/tests/test_stray_output.py
@@ -114,6 +114,7 @@ def test_dtr_and_rts_are_low_before_the_port_opens(self):
         self.assertTrue(make.call_args.kwargs.get("do_not_open"))
         self.assertFalse(t.in_raw_repl)
         self.assertTrue(t.use_raw_paste)
+        self.assertFalse(t.is_pty)  # mpremote 1.29 reads it; a COM port is not a pty
 
     def test_sidecar_holds_lines_low_on_a_uart_bridge_only(self):
         ports = [