diff -urp src.old/winsup/cygwin/thread.cc src/winsup/cygwin/thread.cc
--- src.old/winsup/cygwin/thread.cc	Mon Sep 23 14:15:17 2002
+++ src/winsup/cygwin/thread.cc	Mon Sep 23 14:22:22 2002
@@ -1031,7 +1031,11 @@ void
 pthread_key::run_destructor () const
 {
   if (destructor)
-    destructor (get ());
+    {
+      void *value = get ();
+      if (value)
+        destructor (value);
+    }
 }
 
 /*pshared mutexs: