diff --git a/collects/scheme/sandbox.ss b/collects/scheme/sandbox.ss
index 248636f809..c0837aaa1f 100644
--- a/collects/scheme/sandbox.ss
+++ b/collects/scheme/sandbox.ss
@@ -532,6 +532,7 @@
   (define memory-cust   (make-custodian orig-cust))
   (define memory-cust-box (make-custodian-box memory-cust #t))
   (define user-cust     (make-custodian memory-cust))
+  (define user-cust-box (make-custodian-box user-cust #t))
   (define coverage?     (sandbox-coverage-enabled))
   (define uncovered     #f)
   (define input-ch      (make-channel))
@@ -733,8 +734,15 @@
     ;; must be nested in the above (which is what paramaterize* does), or
     ;; it will not use the new namespace.
     [current-eventspace (make-eventspace)])
-   (set! user-thread (bg-run->thread (run-in-bg user-process)))
-   (set! user-done-evt (handle-evt user-thread (lambda (_) (user-kill) eof)))
+   (let ([t (bg-run->thread (run-in-bg user-process))])
+     (define (on-done _)
+       (terminated! (if (custodian-box-value user-cust-box)
+                      'thread-killed
+                      'custodian-shutdown))
+       (user-kill)
+       eof)
+     (set! user-done-evt (handle-evt t on-done))
+     (set! user-thread t))
    (let ([r (channel-get result-ch)])
      (if (eq? r 'ok)
        ;; initial program executed ok, so return an evaluator
diff --git a/collects/tests/mzscheme/sandbox.ss b/collects/tests/mzscheme/sandbox.ss
index a59909c3bb..8d2c179e71 100644
--- a/collects/tests/mzscheme/sandbox.ss
+++ b/collects/tests/mzscheme/sandbox.ss
@@ -139,7 +139,7 @@
 
    ;; other termination messages
    --top-- (set! ev (make-evaluator 'scheme/base)) (kill-evaluator ev)
-   --eval-- 123 =err> "terminated .evaluator-killed."
+   --eval-- 123 =err> "terminated .evaluator-killed.$"
 
    ;; eval-limits apply to the sandbox creation too
    --top--
@@ -202,9 +202,9 @@
    --top--
    (kill-evaluator ev) => (void)
    --eval--
-   x =err> "terminated .evaluator-killed."
-   y =err> "terminated .evaluator-killed."
-   ,eof =err> "terminated .evaluator-killed."
+   x =err> "terminated .evaluator-killed.$"
+   y =err> "terminated .evaluator-killed.$"
+   ,eof =err> "terminated .evaluator-killed.$"
    --top--
    (let-values ([(i1 o1) (make-pipe)] [(i2 o2) (make-pipe)])
      ;; o1 -> i1 -ev-> o2 -> i2
@@ -417,40 +417,42 @@
    (set! ev (parameterize ([sandbox-eval-limits #f])
               (make-evaluator 'scheme/base)))
    --eval--
-   (kill-thread (current-thread)) =err> "terminated"
+   (kill-thread (current-thread)) =err> "terminated .thread-killed.$"
    --top--
    (set! ev (parameterize ([sandbox-eval-limits #f])
               (make-evaluator 'scheme/base)))
    --eval--
-   (custodian-shutdown-all (current-custodian)) =err> "terminated"
+   (custodian-shutdown-all (current-custodian))
+   =err> "terminated .custodian-shutdown.$"
    --top--
    ;; also happens when it's done directly
    (set! ev (parameterize ([sandbox-eval-limits #f])
               (make-evaluator 'scheme/base)))
    (call-in-sandbox-context ev (lambda () (kill-thread (current-thread))))
-   =err> "terminated"
+   =err> "terminated .thread-killed.$"
    (set! ev (parameterize ([sandbox-eval-limits #f])
               (make-evaluator 'scheme/base)))
    (call-in-sandbox-context ev
      (lambda () (custodian-shutdown-all (current-custodian))))
-   =err> "terminated"
+   =err> "terminated .custodian-shutdown.$"
    --top--
    ;; now make sure it works with per-expression limits too
    (set! ev (make-evaluator 'scheme/base))
    --eval--
-   (kill-thread (current-thread)) =err> "terminated"
+   (kill-thread (current-thread)) =err> "terminated .thread-killed.$"
    --top--
    (set! ev (make-evaluator 'scheme/base))
    --eval--
-   (custodian-shutdown-all (current-custodian)) =err> "terminated"
+   (custodian-shutdown-all (current-custodian))
+   =err> "terminated .custodian-shutdown.$"
    --top--
    (set! ev (make-evaluator 'scheme/base))
    (call-in-sandbox-context ev (lambda () (kill-thread (current-thread))))
-   =err> "terminated"
+   =err> "terminated .thread-killed.$"
    (set! ev (make-evaluator 'scheme/base))
    (call-in-sandbox-context ev
      (lambda () (custodian-shutdown-all (current-custodian))))
-   =err> "terminated"
+   =err> "terminated .custodian-shutdown.$"
 
    ;; when an expression is out of memory, the sandbox should stay alive
    --top--