diff --git a/thread_pthread_mn.c b/thread_pthread_mn.c
index 5c21f212e4..72a5d8fce2 100644
--- a/thread_pthread_mn.c
+++ b/thread_pthread_mn.c
@@ -617,11 +617,17 @@ kqueue_wait(rb_vm_t *vm)
     struct timespec *timeout = NULL;
     int timeout_ms = timer_thread_set_timeout(vm);
 
-    if (timeout_ms >= 0) {
+    if (timeout_ms > 0) {
         calculated_timeout.tv_sec = timeout_ms / 1000;
         calculated_timeout.tv_nsec = (timeout_ms % 1000) * 1000000;
         timeout = &calculated_timeout;
     }
+    else if (timeout_ms == 0) {
+        // Relying on the absence of other members of struct timespec is not strictly portable,
+        // and kevent needs a 0-valued timespec to mean immediate timeout.
+        memset(&calculated_timeout, 0, sizeof(struct timespec));
+        timeout = &calculated_timeout;
+    }
 
     return kevent(timer_th.event_fd, NULL, 0, timer_th.finished_events, KQUEUE_EVENTS_MAX, timeout);
 }