diff --git a/scheme/rts/thread.scm b/scheme/rts/thread.scm
index 9b5a47f..dd77f38 100644
--- a/scheme/rts/thread.scm
+++ b/scheme/rts/thread.scm
@@ -549,6 +549,7 @@
 ; scheduler.
 
 (define (spawn thunk . id)
+  (set-thread-own-values?! (current-thread) #f)
   (apply spawn-on-scheduler
 	 (thread-scheduler (current-thread))
 	 thunk
@@ -557,11 +558,13 @@
 
 (define (spawn-on-root thunk . id)
   (if (root-scheduler)
-      (apply spawn-on-scheduler
-	     (root-scheduler)
-	     thunk
-	     (thread-cell-values (current-thread))
-	     id)
+      (begin
+	(set-thread-own-values?! (current-thread) #f)
+	(apply spawn-on-scheduler
+	       (root-scheduler)
+	       thunk
+	       (thread-cell-values (current-thread))
+	       id))
       (thunk)))
 
 (define (spawn-on-scheduler scheduler thunk cell-values . id)