diff --git a/requests/auth.py b/requests/auth.py
index 618a902a..b950181d 100644
--- a/requests/auth.py
+++ b/requests/auth.py
@@ -67,6 +67,7 @@ class HTTPDigestAuth(AuthBase):
         self.nonce_count = 0
         self.chal = {}
         self.pos = None
+        self.num_401_calls = 1
 
     def build_digest_header(self, method, url):
 
@@ -154,7 +155,7 @@ class HTTPDigestAuth(AuthBase):
     def handle_redirect(self, r, **kwargs):
         """Reset num_401_calls counter on redirects."""
         if r.is_redirect:
-            setattr(self, 'num_401_calls', 1)
+            self.num_401_calls = 1
 
     def handle_401(self, r, **kwargs):
         """Takes the given response and tries digest-auth, if needed."""
@@ -168,7 +169,7 @@ class HTTPDigestAuth(AuthBase):
 
         if 'digest' in s_auth.lower() and num_401_calls < 2:
 
-            setattr(self, 'num_401_calls', num_401_calls + 1)
+            self.num_401_calls += 1
             pat = re.compile(r'digest ', flags=re.IGNORECASE)
             self.chal = parse_dict_header(pat.sub('', s_auth, count=1))
 
@@ -188,7 +189,7 @@ class HTTPDigestAuth(AuthBase):
 
             return _r
 
-        setattr(self, 'num_401_calls', num_401_calls + 1)
+        self.num_401_calls = 1
         return r
 
     def __call__(self, r):