diff --git a/proxy/common/utils.py b/proxy/common/utils.py
index 61a3b9cc..062a567b 100644
--- a/proxy/common/utils.py
+++ b/proxy/common/utils.py
@@ -14,6 +14,7 @@ import socket
 
 from types import TracebackType
 from typing import Optional, Dict, Any, List, Tuple, Type, Callable
+from typing_extensions import Literal
 
 from .constants import HTTP_1_1, COLON, WHITESPACE, CRLF
 
@@ -185,7 +186,7 @@ class socket_connection(contextlib.ContextDecorator):
             self,
             exc_type: Optional[Type[BaseException]],
             exc_val: Optional[BaseException],
-            exc_tb: Optional[TracebackType]) -> bool:
+            exc_tb: Optional[TracebackType]) -> Literal[False]:
         if self.conn:
             self.conn.close()
         return False
diff --git a/proxy/http/parser.py b/proxy/http/parser.py
index efcac32c..a56f1d37 100644
--- a/proxy/http/parser.py
+++ b/proxy/http/parser.py
@@ -117,7 +117,7 @@ class HttpParser:
                 self.host, self.port = self.url.hostname, self.url.port \
                     if self.url.port else 80
             else:
-                raise KeyError('Invalid request\n%s' % self.bytes)
+                raise KeyError(b'Invalid request\n%b' % self.bytes)
             self.path = self.build_url()
 
     def is_chunked_encoded(self) -> bool:
diff --git a/requirements-testing.txt b/requirements-testing.txt
index f1f0886d..a9c8c762 100644
--- a/requirements-testing.txt
+++ b/requirements-testing.txt
@@ -4,6 +4,6 @@ flake8==3.7.9
 pytest==5.2.2
 pytest-cov==2.8.1
 autopep8==1.4.4
-mypy==0.730
+mypy==0.740
 py-spy==0.3.0
 codecov==2.0.15