diff --git a/requests/cookies.py b/requests/cookies.py
index b85fd2b6..eee5168f 100644
--- a/requests/cookies.py
+++ b/requests/cookies.py
@@ -277,6 +277,12 @@ class RequestsCookieJar(cookielib.CookieJar, collections.MutableMapping):
                 dictionary[cookie.name] = cookie.value
         return dictionary
 
+    def __contains__(self, name):
+        try:
+            return super(RequestsCookieJar, self).__contains__(name)
+        except CookieConflictError:
+            return True
+
     def __getitem__(self, name):
         """Dict-like __getitem__() for compatibility with client code. Throws
         exception if there are more than one cookie with name. In that case,
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 1ee379c9..01e88da1 100755
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -754,6 +754,38 @@ class TestRequests:
         # make sure one can use items multiple times
         assert list(items) == list(items)
 
+    def test_cookie_duplicate_names_different_domains(self):
+        key = 'some_cookie'
+        value = 'some_value'
+        domain1 = 'test1.com'
+        domain2 = 'test2.com'
+
+        jar = requests.cookies.RequestsCookieJar()
+        jar.set(key, value, domain=domain1)
+        jar.set(key, value, domain=domain2)
+        assert key in jar
+        items = jar.items()
+        assert len(items) == 2
+
+        # Verify that CookieConflictError is raised if domain is not specified
+        with pytest.raises(requests.cookies.CookieConflictError):
+            jar.get(key)
+
+        # Verify that CookieConflictError is not raised if domain is specified
+        cookie = jar.get(key, domain=domain1)
+        assert cookie == value
+
+    def test_cookie_duplicate_names_raises_cookie_conflict_error(self):
+        key = 'some_cookie'
+        value = 'some_value'
+        path = 'some_path'
+
+        jar = requests.cookies.RequestsCookieJar()
+        jar.set(key, value, path=path)
+        jar.set(key, value)
+        with pytest.raises(requests.cookies.CookieConflictError):
+            jar.get(key)
+
     def test_time_elapsed_blank(self, httpbin):
         r = requests.get(httpbin('get'))
         td = r.elapsed