diff --git a/ChangeLog b/ChangeLog
index 729204ad8e..0479596c53 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Jul 18 23:53:59 2006  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* process.c (rb_f_system): shouldn't block SIGCHLD if it's not
+	  exist.
+
 Tue Jul 18 22:10:13 2006  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* process.c (rb_f_system): block SIGCHLD during the process
diff --git a/process.c b/process.c
index ae9146a928..8d1f07de82 100644
--- a/process.c
+++ b/process.c
@@ -1591,16 +1591,20 @@ static VALUE
 rb_f_system(int argc, VALUE *argv)
 {
     int status;
+#ifdef SIGCHLD
     RETSIGTYPE (*chfunc)(int);
 
     chfunc = signal(SIGCHLD, SIG_DFL);
+#endif
     status = rb_spawn(argc, argv);
     if (status > 0) {
 #if defined(HAVE_FORK) || defined(HAVE_SPAWNV)
 	rb_syswait(status);
 #endif
     }
+#ifdef SIGCHLD
     signal(SIGCHLD, chfunc);
+#endif
     if (status < 0) {
 	rb_sys_fail(RSTRING(argv[0])->ptr);
     }