diff --git a/knots/promise.scm b/knots/promise.scm
index 9df376b..950789c 100644
--- a/knots/promise.scm
+++ b/knots/promise.scm
@@ -82,7 +82,10 @@
                          (make-exception
                           exn
                           (make-knots-exception stack)))))
-                  (fibers-promise-thunk fp)))
+                  (lambda ()
+                    (start-stack
+                     #t
+                     (fibers-promise-thunk fp)))))
               #:unwind? #t))
         (lambda vals
           (atomic-box-set! (fibers-promise-values-box fp)