diff --git a/python/src/trezorlib/transport/session.py b/python/src/trezorlib/transport/session.py
index 7ba6535801..1d0948ddf5 100644
--- a/python/src/trezorlib/transport/session.py
+++ b/python/src/trezorlib/transport/session.py
@@ -154,9 +154,16 @@ class SessionV1(Session):
         resp: messages.Features = self.call_raw(
             messages.Initialize(session_id=session_id, derive_cardano=derive_cardano)
         )
+        if isinstance(self.passphrase, str):
+            self.passphrase_callback = _send_passphrase
         self._id = resp.session_id
 
 
+def _send_passphrase(session: Session, resp: t.Any) -> None:
+    assert isinstance(session.passphrase, str)
+    return session.call(messages.PassphraseAck(passphrase=session.passphrase))
+
+
 def _callback_button(session: Session, msg: t.Any) -> t.Any:
     print("Please confirm action on your Trezor device.")  # TODO how to handle UI?
     return session.call(messages.ButtonAck())