diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index e3d8786cb..591dcfc30 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,15 @@
+2002-09-27  Robert Collins <rbtcollins@hotmail.com>
+
+	* thread.cc (pthread_key::run_destructor): Run_destructor is not
+	const as it needs to set the key value.
+	* thread.h (pthread_key::run_destructor): Ditto.
+
+2002-09-27  Robert Collins <rbtcollins@hotmail.com>
+
+	* thread.cc (pthread_key::run_destructor): Follow opengroup algorithm.
+	I.e. only run the destructor NON-NULL key values, and reset the key
+	to NULL before running the destructor. Reported by Thomas Pfaff.
+
 2002-09-25  Christopher Faylor  <cgf@redhat.com>
 
 	* cygrun.c (main): Fix setting of CYGWIN environment variable.
diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
index 3ee11f1e9..6b05cffb2 100644
--- a/winsup/cygwin/thread.cc
+++ b/winsup/cygwin/thread.cc
@@ -1035,10 +1035,17 @@ pthread_key::recreateKeyFromBuffer ()
 }
 
 void
-pthread_key::run_destructor () const
+pthread_key::run_destructor ()
 {
-  if (destructor)
-    destructor (get ());
+  if (destructor) 
+    {
+      void *oldValue = get();
+      if (oldValue)
+	{
+    	  set (NULL);
+    	  destructor (oldValue);
+	}
+    }
 }
 
 /*pshared mutexs:
diff --git a/winsup/cygwin/thread.h b/winsup/cygwin/thread.h
index c36466020..4be0bf14d 100644
--- a/winsup/cygwin/thread.h
+++ b/winsup/cygwin/thread.h
@@ -212,7 +212,7 @@ private:
   void saveKeyToBuffer ();
   void recreateKeyFromBuffer ();
   void (*destructor) (void *);
-  void run_destructor () const;
+  void run_destructor ();
   void *fork_buf;
 };