diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 85a033c38..0b5ce3f8e 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,12 @@
+Wed Jun 28 19:36:00 2000  Corinna Vinschen <corinna@vinschen.de>
+
+	* syscalls.cc (seteuid): Initialize pi.token before calling
+	internal_getlogin().
+	* uinfo.cc (internal_getlogin): Use impersonation token instead
+	of process token in case of active impersonation. Add some comments.
+	(uinfo_init): Initializing myself->token and myself->impersonated
+	before calling internal_getlogin(). Add some comments.
+
 Mon Jun 26 18:32:41 2000  Christopher Faylor <cgf@cygnus.com>
 
 	* windows.cc (setitimer): Round up when < 1000 usecs.
diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
index 6c40cc153..592e97c47 100644
--- a/winsup/cygwin/syscalls.cc
+++ b/winsup/cygwin/syscalls.cc
@@ -1856,6 +1856,11 @@ seteuid (uid_t uid)
 
           struct pinfo pi;
           pi.psid = (PSID) pi.sidbuf;
+          /* pi.token is used in internal_getlogin() to determine if
+             impersonation is active. If so, the token is used for
+             retrieving user's SID. */
+          pi.token = myself->impersonated ? myself->token
+                                          : INVALID_HANDLE_VALUE;
           struct passwd *pw_cur = getpwnam (internal_getlogin (&pi));
           if (pw_cur != pw_new)
             {
diff --git a/winsup/cygwin/uinfo.cc b/winsup/cygwin/uinfo.cc
index 66bd1aee6..e2d07cc40 100644
--- a/winsup/cygwin/uinfo.cc
+++ b/winsup/cygwin/uinfo.cc
@@ -90,13 +90,18 @@ internal_getlogin (struct pinfo *pi)
         }
       if (allow_ntsec)
         {
-          HANDLE ptok = INVALID_HANDLE_VALUE; 
+          HANDLE ptok = pi->token; /* Which is INVALID_HANDLE_VALUE if no
+                                      impersonation took place. */
           DWORD siz;
           char tu[1024];
           int ret = 0;
             
-          /* Try to get the SID from current process first */
-          if (!OpenProcessToken (GetCurrentProcess (), TOKEN_QUERY, &ptok))
+          /* Try to get the SID either from already impersonated token
+             or from current process first. To differ that two cases is
+             important, because you can't rely on the user information
+             in a process token of a currently impersonated process. */
+          if (ptok == INVALID_HANDLE_VALUE
+              && !OpenProcessToken (GetCurrentProcess (), TOKEN_QUERY, &ptok))
             debug_printf ("OpenProcessToken(): %E\n");
           else if (!GetTokenInformation (ptok, TokenUser, (LPVOID) &tu,
                                          sizeof tu, &siz))
@@ -104,7 +109,8 @@ internal_getlogin (struct pinfo *pi)
           else if (!(ret = CopySid (40, (PSID) pi->sidbuf,
                                     ((TOKEN_USER *) &tu)->User.Sid)))
             debug_printf ("Couldn't retrieve SID from access token!");
-          if (ptok != INVALID_HANDLE_VALUE)
+          /* Close token only if it's a result from OpenProcessToken(). */
+          if (ptok != INVALID_HANDLE_VALUE && pi->token == INVALID_HANDLE_VALUE)
             CloseHandle (ptok);
 
           /* If that failes, try to get the SID from localhost. This can only
@@ -164,6 +170,13 @@ uinfo_init ()
   char *username;
   struct passwd *p;
 
+  /* Initialize to non impersonated values.
+     Setting `impersonated' to TRUE seems to be wrong but it
+     isn't. Impersonated is thought as "Current User and `token'
+     are coincident". See seteuid() for the mechanism behind that. */
+  myself->token = INVALID_HANDLE_VALUE;
+  myself->impersonated = TRUE;
+
   /* If psid is non null, the process is forked or spawned from
      another cygwin process without changing the user context.
      So all user infos in myself as well as the environment are
@@ -179,7 +192,6 @@ uinfo_init ()
     {
       /* calling getpwnam assures us that /etc/password has been
          read in, but we can't be sure about /etc/group */
-
       if (!group_in_memory_p)
         read_etc_group ();
 
@@ -191,9 +203,8 @@ uinfo_init ()
       myself->uid = DEFAULT_UID;
       myself->gid = DEFAULT_GID;
     }
-  /* Set to non impersonated value. */
-  myself->token = INVALID_HANDLE_VALUE;
-  myself->impersonated = TRUE;
+  /* Real and effective uid/gid are always identical on process start up.
+     This is at least true for NT/W2K. */
   myself->orig_uid = myself->real_uid = myself->uid;
   myself->orig_gid = myself->real_gid = myself->gid;
 }