diff --git a/modal/io_streams.py b/modal/io_streams.py
index ebea695e4..59d2f8008 100644
--- a/modal/io_streams.py
+++ b/modal/io_streams.py
@@ -1,6 +1,18 @@
 # Copyright Modal Labs 2022
 import asyncio
-from typing import TYPE_CHECKING, AsyncGenerator, Generic, List, Literal, Optional, Tuple, TypeVar, Union
+from typing import (
+    TYPE_CHECKING,
+    AsyncGenerator,
+    AsyncIterator,
+    Generic,
+    List,
+    Literal,
+    Optional,
+    Tuple,
+    TypeVar,
+    Union,
+    cast,
+)
 
 from grpclib import Status
 from grpclib.exceptions import GRPCError, StreamTerminatedError
@@ -18,7 +30,7 @@
 
 
 async def _sandbox_logs_iterator(
-    sandbox_id: str, file_descriptor: int, last_entry_id: Optional[str], client: _Client
+    sandbox_id: str, file_descriptor: "api_pb2.FileDescriptor.ValueType", last_entry_id: str, client: _Client
 ) -> AsyncGenerator[Tuple[Optional[bytes], str], None]:
     req = api_pb2.SandboxGetLogsRequest(
         sandbox_id=sandbox_id,
@@ -37,7 +49,7 @@ async def _sandbox_logs_iterator(
 
 
 async def _container_process_logs_iterator(
-    process_id: str, file_descriptor: int, client: _Client
+    process_id: str, file_descriptor: "api_pb2.FileDescriptor.ValueType", client: _Client
 ) -> AsyncGenerator[Optional[bytes], None]:
     req = api_pb2.ContainerExecGetOutputRequest(
         exec_id=process_id, timeout=55, file_descriptor=file_descriptor, get_raw_bytes=True
@@ -74,9 +86,11 @@ class _StreamReader(Generic[T]):
     ```
     """
 
+    _stream: Optional[AsyncGenerator[Optional[bytes], None]]
+
     def __init__(
         self,
-        file_descriptor: int,
+        file_descriptor: "api_pb2.FileDescriptor.ValueType",
         object_id: str,
         object_type: Literal["sandbox", "container_process"],
         client: _Client,
@@ -90,7 +104,7 @@ def __init__(
         self._object_id = object_id
         self._client = client
         self._stream = None
-        self._last_entry_id: Optional[str] = None
+        self._last_entry_id: str = ""
         self._line_buffer = b""
 
         # Sandbox logs are streamed to the client as strings, so StreamReaders reading
@@ -145,15 +159,20 @@ async def read(self) -> T:
         ```
 
         """
-        data = "" if self._text else b""
+        data_str = ""
+        data_bytes = b""
         async for message in self._get_logs():
             if message is None:
                 break
             if self._text:
-                data += message.decode("utf-8")
+                data_str += message.decode("utf-8")
             else:
-                data += message
-        return data
+                data_bytes += message
+
+        if self._text:
+            return cast(T, data_str)
+        else:
+            return cast(T, data_bytes)
 
     async def _consume_container_process_stream(self):
         """
@@ -275,7 +294,7 @@ async def _get_logs_by_line(self) -> AsyncGenerator[Optional[bytes], None]:
                     line, self._line_buffer = self._line_buffer.split(b"\n", 1)
                     yield line + b"\n"
 
-    def __aiter__(self) -> AsyncGenerator[T, None]:
+    def __aiter__(self) -> AsyncIterator[T]:
         """mdmd:hidden"""
         if not self._stream:
             if self._by_line:
@@ -287,6 +306,7 @@ def __aiter__(self) -> AsyncGenerator[T, None]:
     async def __anext__(self) -> T:
         """mdmd:hidden"""
         assert self._stream is not None
+
         value = await self._stream.__anext__()
 
         # The stream yields None if it receives an EOF batch.
@@ -294,9 +314,9 @@ async def __anext__(self) -> T:
             raise StopAsyncIteration
 
         if self._text:
-            return value.decode("utf-8")
+            return cast(T, value.decode("utf-8"))
         else:
-            return value
+            return cast(T, value)
 
 
 MAX_BUFFER_SIZE = 2 * 1024 * 1024
diff --git a/tasks.py b/tasks.py
index ebbede6f5..954b3faef 100644
--- a/tasks.py
+++ b/tasks.py
@@ -149,6 +149,7 @@ def type_check(ctx):
         "modal/_utils/shell_utils.py",
         "test/cls_test.py",  # see mypy bug above - but this works with pyright, so we run that instead
         "modal/_container_io_manager.py",
+        "modal/io_streams.py",
     ]
     ctx.run(f"pyright {' '.join(pyright_allowlist)}", pty=True)