diff --git a/nvchecker/httpclient/base.py b/nvchecker/httpclient/base.py
index b343a6c..13d16bc 100644
--- a/nvchecker/httpclient/base.py
+++ b/nvchecker/httpclient/base.py
@@ -121,4 +121,4 @@ class TemporaryError(BaseHTTPError):
   '''A temporary error (e.g. network error) happens.'''
 
 class HTTPError(BaseHTTPError):
-  ''' An HTTP 4xx error happens '''
+  '''An HTTP 4xx error happens'''