--- a/src/runtime/darwin-os.c
+++ b/src/runtime/darwin-os.c
@@ -29,6 +29,12 @@
 #include <mach/mach.h>
 #include <libkern/OSAtomic.h>
 #include <stdlib.h>
+#endif
+
+#if defined(LISP_FEATURE_SB_WTIMER)
+# include <sys/types.h>
+# include <sys/event.h>
+# include <sys/time.h>
 #endif
 
 char *
@@ -301,3 +307,71 @@
 }
 
 #endif
+
+#if defined(LISP_FEATURE_SB_WTIMER)
+
+# error Completely untested. Go ahead! Remove this line, try your luck!
+
+/*
+ * Waitable timer implementation for the safepoint-based (SIGALRM-free)
+ * timer facility using kqueue.
+ *
+ * Unlike FreeBSD with its ms (!) timer resolution, Darwin supports ns
+ * timer resolution -- or at least it pretends to do so on the API
+ * level (?).  To use it, we need the *64 versions of the functions and
+ * structures.
+ *
+ * Unfortunately, I don't run Darwin, and can't test this code, so it's
+ * just a hopeful translation from FreeBSD.
+ */
+
+int
+os_create_wtimer()
+{
+    int kq = kqueue();
+    if (kq == -1)
+        lose("os_create_wtimer: kqueue");
+    return kq;
+}
+
+int
+os_wait_for_wtimer(int kq)
+{
+    struct kevent64_s ev;
+    int n;
+    if ( (n = kevent64(kq, 0, 0, &ev, 1, 0, 0)) == -1) {
+        if (errno != EINTR)
+            lose("os_wtimer_listen failed");
+        n = 0;
+    }
+    return n != 1;
+}
+
+void
+os_close_wtimer(int kq)
+{
+    if (close(kq) == -1)
+        lose("os_close_wtimer failed");
+}
+
+void
+os_set_wtimer(int kq, int sec, int nsec)
+{
+    int64_t nsec = ((int64_t) sec) * 1000000000 + (int64_t) nsec;
+
+    struct kevent64_s ev;
+    EV_SET64(&ev, 1, EVFILT_TIMER, EV_ADD|EV_ENABLE|EV_ONESHOT, NOTE_NSECONDS,
+             nsec, 0, 0, 0);
+    if (kevent64(kq, &ev, 1, 0, 0, 0, 0) == -1)
+        perror("os_set_wtimer: kevent");
+}
+
+void
+os_cancel_wtimer(int kq)
+{
+    struct kevent64_s ev;
+    EV_SET64(&ev, 1, EVFILT_TIMER, EV_DISABLE, 0, 0, 0, 0, 0);
+    if (kevent64(kq, &ev, 1, 0, 0, 0, 0) == -1 && errno != ENOENT)
+        perror("os_cancel_wtimer: kevent");
+}
+#endif