diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 5ab8a2a6a..c265b202f 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,8 @@
+2012-05-29  Corinna Vinschen  <corinna@vinschen.de>
+
+	* security.h (cygsidlist::+=): Correctly copy well_known_sid info from
+	source cygsid.
+
 2012-05-25  Corinna Vinschen  <corinna@vinschen.de>
 
 	* registry.cc (reg_key::build_reg): Fix typo in debug output.
diff --git a/winsup/cygwin/security.h b/winsup/cygwin/security.h
index 6629260d2..907cbe766 100644
--- a/winsup/cygwin/security.h
+++ b/winsup/cygwin/security.h
@@ -1,7 +1,7 @@
 /* security.h: security declarations
 
    Copyright 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
-   2010, 2011 Red Hat, Inc.
+   2010, 2011, 2012 Red Hat, Inc.
 
 This file is part of Cygwin.
 
@@ -223,9 +223,12 @@ public:
 
   /* += adds a "normal" SID, *= adds a well-known SID.  See comment in class
      cygsid above. */
-  BOOL operator+= (cygsid &si) { return add ((PSID) si, false); }
+  BOOL operator+= (cygsid &si) { return add ((PSID) si,
+					     si.is_well_known_sid ()); }
   BOOL operator+= (const char *sidstr) { cygsid nsi (sidstr);
-					 return add ((PSID) nsi, false); }
+					 return add ((PSID) nsi,
+						     nsi.is_well_known_sid ());
+				       }
   BOOL operator+= (const PSID psid) { return add (psid, false); }
   BOOL operator*= (cygsid &si) { return add ((PSID) si, true); }
   BOOL operator*= (const char *sidstr) { cygsid nsi (sidstr);