diff --git a/src/prompt_toolkit/application/application.py b/src/prompt_toolkit/application/application.py
index 5e9c6a997..b98d986ff 100644
--- a/src/prompt_toolkit/application/application.py
+++ b/src/prompt_toolkit/application/application.py
@@ -23,6 +23,7 @@
 from typing import (
     Any,
     Generic,
+    Literal,
     TypeVar,
     cast,
     overload,
@@ -1055,7 +1056,10 @@ def _breakpointhook(self, *a: object, **kw: object) -> None:
         import pdb
         from types import FrameType
 
-        TraceDispatch = Callable[[FrameType, str, Any], Any]
+        TraceDispatch = Callable[
+            [FrameType, Literal["call", "line", "return", "exception", "opcode"], Any],
+            Any,
+        ]
 
         @contextmanager
         def hide_app_from_eventloop_thread() -> Generator[None, None, None]:
diff --git a/src/prompt_toolkit/contrib/telnet/protocol.py b/src/prompt_toolkit/contrib/telnet/protocol.py
index e56edd1ca..56e31035f 100644
--- a/src/prompt_toolkit/contrib/telnet/protocol.py
+++ b/src/prompt_toolkit/contrib/telnet/protocol.py
@@ -135,7 +135,7 @@ def ttype(self, data: bytes) -> None:
         """
         subcmd, data = data[0:1], data[1:]
         if subcmd == IS:
-            ttype = data.decode("ascii")
+            ttype = data.decode("ascii", errors="replace")
             self.ttype_received_callback(ttype)
         else:
             logger.warning("Received a non-IS terminal type Subnegotiation")