diff --git a/collects/tests/mzscheme/quiet.ss b/collects/tests/mzscheme/quiet.ss
index c35ae16081..1956da38fb 100644
--- a/collects/tests/mzscheme/quiet.ss
+++ b/collects/tests/mzscheme/quiet.ss
@@ -5,6 +5,8 @@
       (let ([argv (current-command-line-arguments)])
         (if (= 1 (vector-length argv)) (vector-ref argv 0) "all.ss")))))
 
+(define timeout-thread #f)
+
 (namespace-variable-value 'real-error-port #f
   (lambda ()
     (let ([err  (current-error-port)]
@@ -23,13 +25,15 @@
                                       (set! last-error e))
                                     (errh e)))
       ;; -- set up a timeout
-      (thread (lambda ()
-                (sleep 900)
-                (fprintf err "\n\n~aTIMEOUT -- ABORTING!\n" Section-prefix)
-                (exit 3)
-                ;; in case the above didn't work for some reason
-                (sleep 60)
-                (custodian-shutdown-all cust))))))
+      (set! timeout-thread
+            (thread
+             (lambda ()
+               (sleep 1200)
+               (fprintf err "\n\n~aTIMEOUT -- ABORTING!\n" Section-prefix)
+               (exit 3)
+               ;; in case the above didn't work for some reason
+               (sleep 60)
+               (custodian-shutdown-all cust)))))))
 
 (let ([p (make-output-port
           'quiet always-evt (lambda (str s e nonblock? breakable?) (- e s))
@@ -37,7 +41,8 @@
   (call-with-continuation-prompt
    (lambda ()
      (parameterize ([current-output-port p] [current-error-port p])
-       (load-relative quiet-load)))
+       (load-relative quiet-load))
+     (kill-thread timeout-thread))
    (default-continuation-prompt-tag)
    (lambda (thunk)
      (when last-error
diff --git a/collects/tests/run-automated-tests.ss b/collects/tests/run-automated-tests.ss
index 2df9b00213..b0978b659b 100755
--- a/collects/tests/run-automated-tests.ss
+++ b/collects/tests/run-automated-tests.ss
@@ -64,8 +64,9 @@
         (set! exit-code (max exit-code n))
         (echo "BOOM!") ; used to find errors in nightly builds
         (break)))
-    (thread (let ([th (current-thread)])
-              (lambda () (sleep 900) (echo "Timeout!") (break-thread th))))
+    (define timeout-thread
+      (thread (let ([th (current-thread)])
+                (lambda () (sleep 1200) (echo "Timeout!") (break-thread th)))))
     (parameterize* ([exit-handler
                      (lambda (n) (abort n "exit with error code ~a" n))]
                     [current-namespace (make-base-empty-namespace)])
@@ -78,6 +79,7 @@
           (with-handlers ([void (lambda (exn)
                                   (abort 1 "error: ~a" (exn-message exn)))])
             (thunk))))
+      (kill-thread timeout-thread)
       (echo "all tests passed."))))
 
 (exit exit-code)