diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index bc701fd5a..9f36db5a9 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,9 @@
+2007-08-16  Corinna Vinschen  <corinna@vinschen.de>
+
+	* ntdll.h (RtlAcquirePebLock): Declare.
+	(RtlReleasePebLock): Declare.
+	* path.cc (cwdstuff::set): Change PEB only while it's locked.
+
 2007-08-16  Corinna Vinschen  <corinna@vinschen.de>
 
 	* fhandler.h (fhandler_base::get_namehash): Use NT native path.
diff --git a/winsup/cygwin/ntdll.h b/winsup/cygwin/ntdll.h
index 7b8c556b9..ff9f95506 100644
--- a/winsup/cygwin/ntdll.h
+++ b/winsup/cygwin/ntdll.h
@@ -827,6 +827,7 @@ extern "C"
   NTSTATUS NTAPI RtlAppendUnicodeToString (PUNICODE_STRING, PCWSTR);
   NTSTATUS NTAPI RtlAppendUnicodeStringToString (PUNICODE_STRING,
 						 PUNICODE_STRING);
+  VOID NTAPI RtlAcquirePebLock ();
   NTSTATUS NTAPI RtlAnsiStringToUnicodeString (PUNICODE_STRING, PANSI_STRING,
 					       BOOLEAN);
   LONG NTAPI RtlCompareUnicodeString (PUNICODE_STRING, PUNICODE_STRING,
@@ -848,6 +849,7 @@ extern "C"
 					       BOOLEAN);
   BOOLEAN NTAPI RtlPrefixUnicodeString (PUNICODE_STRING, PUNICODE_STRING,
 					BOOLEAN);
+  VOID NTAPI RtlReleasePebLock ();
   VOID NTAPI RtlSecondsSince1970ToTime (ULONG, PLARGE_INTEGER);
   NTSTATUS NTAPI RtlUnicodeStringToAnsiString (PANSI_STRING, PUNICODE_STRING,
 					       BOOLEAN);
diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index 5a0bc903b..a8b64da98 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -4329,6 +4329,7 @@ cwdstuff::set (const char *win32_cwd, const char *posix_cwd, bool doit)
 	      strcpy (as.Buffer + len, "\\");
 	      ++as.Length;
 	    }
+	  RtlAcquirePebLock ();
 	  if (current_codepage == ansi_cp)
 	    RtlAnsiStringToUnicodeString (
 			&get_user_proc_parms ()->CurrentDirectoryName,
@@ -4339,11 +4340,9 @@ cwdstuff::set (const char *win32_cwd, const char *posix_cwd, bool doit)
 			&as, FALSE);
 	  PHANDLE phdl = &get_user_proc_parms ()->CurrentDirectoryHandle;
 	  if (*phdl)
-	    {
-	      HANDLE old_h = *phdl;
-	      *phdl = h;
-	      CloseHandle (old_h);
-	    }
+	    CloseHandle (*phdl);
+	  *phdl = h;
+	  RtlReleasePebLock ();
 	}
     }
   /* If there is no win32 path or it has the form c:xxx, get the value */