diff --git a/adafruit_ble_file_transfer.py b/adafruit_ble_file_transfer.py
index 7ee1932..cc70878 100644
--- a/adafruit_ble_file_transfer.py
+++ b/adafruit_ble_file_transfer.py
@@ -65,7 +65,7 @@ def __init__(self) -> None:
             fixed_length=False,
         )
 
-    def bind(self, service: Service) -> _bleio.PacketBuffer:
+    def bind(self, service: "FileTransferService") -> _bleio.PacketBuffer:
         """Binds the characteristic to the given Service."""
         bound_characteristic = super().bind(service)
         return _bleio.PacketBuffer(