diff --git a/Lib/Cookie.py b/Lib/Cookie.py
index e1eb734..b2f7427 100644
--- a/Lib/Cookie.py
+++ b/Lib/Cookie.py
@@ -408,6 +408,9 @@
     # For historical reasons, these attributes are also reserved:
     #   expires
     #
+    # This is an extension from Microsoft:
+    #   httponly
+    #
     # This dictionary provides a mapping from the lowercase
     # variant on the left to the appropriate traditional
     # formatting on the right.
@@ -417,6 +420,7 @@
                    "domain"      : "Domain",
                    "max-age" : "Max-Age",
                    "secure"      : "secure",
+                   "httponly"  : "httponly",
                    "version" : "Version",
                    }
 
@@ -499,6 +503,8 @@
                 RA("%s=%d" % (self._reserved[K], V))
             elif K == "secure":
                 RA(str(self._reserved[K]))
+            elif K == "httponly":
+                RA(str(self._reserved[K]))
             else:
                 RA("%s=%s" % (self._reserved[K], V))