diff --git a/ChangeLog b/ChangeLog
index 801ac5d40b..5bd8c35d01 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+Wed Aug 29 23:42:59 2012  Tanaka Akira  <akr@fsij.org>
+
+	* internal.h (rb_last_status_clear): declared.
+
+	* process.c (rb_last_status_clear): exported.
+	  (rb_f_system): call rb_last_status_clear.
+
+	* io.c (rb_f_backquote): call rb_last_status_clear.
+
 Wed Aug 29 22:01:15 2012  Tanaka Akira  <akr@fsij.org>
 
 	* process.c (rb_f_system): check failures of waitpid.
diff --git a/internal.h b/internal.h
index ed4864c1eb..57c1fc8cfa 100644
--- a/internal.h
+++ b/internal.h
@@ -222,6 +222,7 @@ struct rb_execarg {
 #define ARGVSTR2ARGV(argv_str) ((char **)RSTRING_PTR(argv_str) + 1)
 
 rb_pid_t rb_fork_ruby(int *status);
+void rb_last_status_clear(void);
 
 /* rational.c */
 VALUE rb_lcm(VALUE x, VALUE y);
diff --git a/io.c b/io.c
index b1a38cc707..4b6851b44d 100644
--- a/io.c
+++ b/io.c
@@ -7808,6 +7808,7 @@ rb_f_backquote(VALUE obj, VALUE str)
     rb_io_t *fptr;
 
     SafeStringValue(str);
+    rb_last_status_clear();
     port = pipe_open_s(str, "r", FMODE_READABLE|DEFAULT_TEXTMODE, NULL);
     if (NIL_P(port)) return rb_str_new(0,0);
 
diff --git a/process.c b/process.c
index 25eed71a4e..e0bb84a4d2 100644
--- a/process.c
+++ b/process.c
@@ -226,7 +226,7 @@ rb_last_status_set(int status, rb_pid_t pid)
     rb_iv_set(th->last_status, "pid", PIDT2NUM(pid));
 }
 
-static void
+void
 rb_last_status_clear(void)
 {
     GET_THREAD()->last_status = Qnil;
@@ -3656,6 +3656,7 @@ rb_f_system(int argc, VALUE *argv)
 #ifdef SIGCHLD
     RETSIGTYPE (*chfunc)(int);
 
+    rb_last_status_clear();
     chfunc = signal(SIGCHLD, SIG_DFL);
 #endif
     pid = rb_spawn_internal(argc, argv, NULL, 0);