Index: process.c
===================================================================
--- process.c	(revision 26425)
+++ process.c	(working copy)
@@ -1331,11 +1331,11 @@
     fflush(stderr);
 #endif
 
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__APPLE__)
     before_exec();
 #endif
     pid = fork();
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__APPLE__)
     after_exec();
 #endif
     switch (pid) {
@@ -1578,7 +1578,7 @@
 
     chfunc = signal(SIGCHLD, SIG_DFL);
   retry:
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__APPLE__)
     before_exec();
 #endif
     pid = fork();
@@ -1588,7 +1588,7 @@
 	rb_protect(proc_exec_args, (VALUE)&earg, NULL);
 	_exit(127);
     }
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__APPLE__)
     after_exec();
 #endif
     if (pid < 0) {
Index: eval.c
===================================================================
--- eval.c	(revision 26425)
+++ eval.c	(working copy)
@@ -12520,7 +12520,7 @@
     safe_mutex_lock(&time_thread.lock);
     if (pthread_create(&time_thread.thread, 0, thread_timer, args) == 0) {
 	thread_init = 1;
-#ifndef __NetBSD__
+#if !defined(__NetBSD__) && !defined(__APPLE__)
 	pthread_atfork(0, 0, rb_thread_stop_timer);
 #endif
 	pthread_cond_wait(&start, &time_thread.lock);
Index: io.c
===================================================================
--- io.c	(revision 26425)
+++ io.c	(working copy)
@@ -3267,7 +3267,7 @@
     }
 
   retry:
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__APPLE__)
     rb_thread_stop_timer();
 #endif
     switch ((pid = fork())) {
@@ -3297,7 +3297,7 @@
 		    ruby_sourcefile, ruby_sourceline, pname);
 	    _exit(127);
 	}
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__APPLE__)
 	rb_thread_start_timer();
 #endif
 	rb_io_synchronized(RFILE(orig_stdout)->fptr);
@@ -3305,7 +3305,7 @@
 	return Qnil;
 
       case -1:			/* fork failed */
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__APPLE__)
 	rb_thread_start_timer();
 #endif
 	if (errno == EAGAIN) {
@@ -3328,7 +3328,7 @@
 	break;
 
       default:			/* parent */
-#ifdef __NetBSD__
+#if defined(__NetBSD__) || defined(__APPLE__)
 	rb_thread_start_timer();
 #endif
 	if (pid < 0) rb_sys_fail(pname);