diff --git a/requests/cookies.py b/requests/cookies.py
index 4d1708d4..a53f2104 100644
--- a/requests/cookies.py
+++ b/requests/cookies.py
@@ -45,10 +45,14 @@ class MockRequest(object):
         return self.get_host()
 
     def get_full_url(self):
+        # Only return the response's URL if the user hadn't set the Host
+        # header
         if not self._r.headers.get('Host'):
             return self._r.url
+        # If they did set it, retrieve it and reconstruct the expected doain
         host = self._r.headers['Host']
         parsed = urlparse(self._r.url)
+        # Reconstruct the URL as we expect it
         return urlunparse([
             parsed.scheme, host, parsed.path, parsed.params, parsed.query,
             parsed.fragment