diff --git a/paradox/interfaces/text/gsm.py b/paradox/interfaces/text/gsm.py
index 36ae872..229e831 100644
--- a/paradox/interfaces/text/gsm.py
+++ b/paradox/interfaces/text/gsm.py
@@ -2,6 +2,7 @@
 import json
 import logging
 import os
+from typing import Callable, Optional
 
 import serial_asyncio
 
@@ -90,7 +91,7 @@ def on_message(self, message: bytes):
         else:
             self.queue.put_nowait(message)
 
-    def set_recv_callback(self, callback):
+    def set_recv_callback(self, callback: Optional[Callable[[str], bool]]):
         self.recv_callback = callback
 
     def open_timeout(self):
@@ -219,7 +220,7 @@ async def run(self):
 
             await asyncio.sleep(5)
 
-    async def data_received(self, data: str) -> bool:
+    def data_received(self, data: str) -> bool:
         logger.debug(f"Data Received: {data}")
 
         data = data.decode()
diff --git a/tests/interfaces/test_gsm.py b/tests/interfaces/test_gsm.py
index 89406b3..efc2a7e 100644
--- a/tests/interfaces/test_gsm.py
+++ b/tests/interfaces/test_gsm.py
@@ -104,7 +104,7 @@ async def control_partition(partition, command):
     interface.modem_connected = True
 
     data = b"+CMT: test_data"
-    await interface.data_received(data)
+    interface.data_received(data)
     assert interface.message_cmt == data.decode()
 
     # level = EventLevel.INFO