diff --git a/racket/src/io/network/address.rkt b/racket/src/io/network/address.rkt
index 3aa881d5ed..cbba88e2a8 100644
--- a/racket/src/io/network/address.rkt
+++ b/racket/src/io/network/address.rkt
@@ -34,7 +34,7 @@
       (lambda (lookup-box)
         (define lookup (unbox lookup-box))
         (when lookup
-          (rktio_addrinfo_lookup_stop lookup)))
+          (rktio_addrinfo_lookup_stop rktio lookup)))
       ;; in atomic mode
       (lambda (lookup-box)
         (define lookup (unbox lookup-box))
diff --git a/racket/src/io/sandman/ltps.rkt b/racket/src/io/sandman/ltps.rkt
index 67f2eef2c1..a90d1c513a 100644
--- a/racket/src/io/sandman/ltps.rkt
+++ b/racket/src/io/sandman/ltps.rkt
@@ -8,7 +8,7 @@
          shared-ltps-place-init!
 
          fd-semaphore-update!
-         fd-semaphore-poll-ready)
+         fd-semaphore-poll-ready?)
 
 (define (make-ltps)
   (define ltps (rktio_ltps_open rktio))
@@ -63,18 +63,18 @@
            s])])]))
 
 ;; in atomic mode
-(define (fd-semaphore-poll-ready)
+(define (fd-semaphore-poll-ready?)
   (unless (eq? shared-ltps rktio_NULL)
     (rktio_ltps_poll rktio shared-ltps)
-    (let loop ()
+    (let loop ([did? #f])
       (define h (rktio_ltps_get_signaled_handle rktio shared-ltps))
       (cond
         [(rktio-error? h)
          ;; Could log an error that isn't RKTIO_ERROR_LTPS_NOT_FOUND
-         (void)]
+         did?]
         [else
          (define ib (address->immobile-cell (rktio_ltps_handle_get_data rktio h)))
          (semaphore-post-all (immobile-cell-ref ib))
          (free-immobile-cell ib)
          (rktio_free h)
-         (loop)]))))
+         (loop #t)]))))
diff --git a/racket/src/io/sandman/main.rkt b/racket/src/io/sandman/main.rkt
index 83f6d73f31..8d9bd41c08 100644
--- a/racket/src/io/sandman/main.rkt
+++ b/racket/src/io/sandman/main.rkt
@@ -97,7 +97,8 @@
                                         [(eqv? v RKTIO_OS_SIGNAL_TERM) 'terminate]
                                         [else 'break]))
            (check-signals)))
-       (fd-semaphore-poll-ready)
+       (when (fd-semaphore-poll-ready?)
+         (wakeup #f))
        ((sandman-do-poll timeout-sandman) mode wakeup))
 
      ;; get-wakeup
diff --git a/racket/src/thread/sandman.rkt b/racket/src/thread/sandman.rkt
index c2a439bc83..1755036e7d 100644
--- a/racket/src/thread/sandman.rkt
+++ b/racket/src/thread/sandman.rkt
@@ -61,6 +61,9 @@
   ((sandman-do-remove-thread! the-sandman) th h))
 
 ;; in atomic mode
+;; The `thread-wakeup` callback can be called with #f
+;; to indicate that a thread was potentially woken up
+;; some other way, such as by a semaphore post
 (define (sandman-poll mode thread-wakeup)
   ((sandman-do-poll the-sandman) mode thread-wakeup))
 
diff --git a/racket/src/thread/schedule.rkt b/racket/src/thread/schedule.rkt
index b749918807..46a4e06971 100644
--- a/racket/src/thread/schedule.rkt
+++ b/racket/src/thread/schedule.rkt
@@ -174,7 +174,8 @@
   (define did? #f)
   (sandman-poll mode
                 (lambda (t)
-                  (thread-reschedule! t)
+                  (when t
+                    (thread-reschedule! t))
                   (set! did? #t)))
   (when did?
     (thread-did-work!))