diff --git a/client/src/telethon/_impl/mtsender/sender.py b/client/src/telethon/_impl/mtsender/sender.py
index b8d3ca8a..fbc42a32 100644
--- a/client/src/telethon/_impl/mtsender/sender.py
+++ b/client/src/telethon/_impl/mtsender/sender.py
@@ -240,7 +240,7 @@ class Sender:
     async def step(self) -> None:
         if not self._writing:
             self._writing = True
-            self._try_fill_write()
+            await self._try_fill_write()
             self._writing = False
 
         if not self._reading:
@@ -265,7 +265,7 @@ class Sender:
         else:
             self._on_net_read(recv_data)
 
-    def _try_fill_write(self) -> None:
+    async def _try_fill_write(self) -> None:
         for request in self._requests:
             if isinstance(request.state, NotSerialized):
                 if (msg_id := self._mtp.push(request.body)) is not None:
@@ -282,6 +282,8 @@ class Sender:
                 if isinstance(request.state, Serialized):
                     request.state = Sent(request.state.msg_id, container_msg_id)
 
+            await self._writer.drain()
+
     def _on_net_read(self, read_buffer: bytes) -> None:
         if not read_buffer:
             raise ConnectionResetError("read 0 bytes")