diff --git a/aiohttp/web_urldispatcher.py b/aiohttp/web_urldispatcher.py
index 150f1449ed..dc7005d32d 100644
--- a/aiohttp/web_urldispatcher.py
+++ b/aiohttp/web_urldispatcher.py
@@ -758,7 +758,7 @@ class MaskDomain(Domain):
 
     def __init__(self, domain: str) -> None:
         super().__init__(domain)
-        mask = self._domain.replace('.', '\.').replace('*', '.*')
+        mask = self._domain.replace('.', r'\.').replace('*', '.*')
         self._mask = re.compile(mask)
 
     @property
diff --git a/requirements/flake.txt b/requirements/flake.txt
index d4b0e33e4f..df6fd48117 100644
--- a/requirements/flake.txt
+++ b/requirements/flake.txt
@@ -1,2 +1,2 @@
-flake8==3.5.0
+flake8==3.6.0
 isort==4.3.4
diff --git a/setup.cfg b/setup.cfg
index ca375585a7..58f711eb0d 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -11,7 +11,7 @@ max-line-length=79
 zip_ok = false
 
 [flake8]
-ignore = N801,N802,N803,E226
+ignore = N801,N802,N803,E226,W504,E252
 max-line-length=79
 
 [isort]