diff --git a/aiohttp/abc.py b/aiohttp/abc.py
index bfea03ff12a..feeb3ad65c9 100644
--- a/aiohttp/abc.py
+++ b/aiohttp/abc.py
@@ -191,8 +191,8 @@ def filter_cookies(self, request_url: URL) -> "BaseCookie[str]":
 class AbstractStreamWriter(ABC):
     """Abstract stream writer."""
 
-    buffer_size = 0
-    output_size = 0
+    buffer_size: int = 0
+    output_size: int = 0
     length: Optional[int] = 0
 
     @abstractmethod
diff --git a/aiohttp/http_writer.py b/aiohttp/http_writer.py
index c6c80edc3c4..c66fda3d8d0 100644
--- a/aiohttp/http_writer.py
+++ b/aiohttp/http_writer.py
@@ -38,6 +38,12 @@ class HttpVersion(NamedTuple):
 
 
 class StreamWriter(AbstractStreamWriter):
+
+    length: Optional[int] = None
+    chunked: bool = False
+    _eof: bool = False
+    _compress: Optional[ZLibCompressor] = None
+
     def __init__(
         self,
         protocol: BaseProtocol,
@@ -46,17 +52,7 @@ def __init__(
         on_headers_sent: _T_OnHeadersSent = None,
     ) -> None:
         self._protocol = protocol
-
         self.loop = loop
-        self.length = None
-        self.chunked = False
-        self.buffer_size = 0
-        self.output_size = 0
-
-        self._eof = False
-        self._compress: Optional[ZLibCompressor] = None
-        self._drain_waiter = None
-
         self._on_chunk_sent: _T_OnChunkSent = on_chunk_sent
         self._on_headers_sent: _T_OnHeadersSent = on_headers_sent