a.diff

diff --git a/ChangeLog b/ChangeLog
index fb54b94..707c638 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Tue Sep 10 10:39:24 2013  Shota Fukumori  <her@sorah.jp>
+
+	* vm_backtrace.c (vm_backtrace_to_ary): Ignore the second argument if
+	  it is nil. [Bug #8884] [ruby-core:57094]
+
+	* test/ruby/test_backtrace.rb (test_caller_with_nil_length):
+	  Test for above.
+
 Tue Sep 10 10:08:00 2013  Kazuhiro NISHIYAMA  <zn@mbf.nifty.com>
 
 	* NEWS: Update RubyGems note.
diff --git a/test/ruby/test_backtrace.rb b/test/ruby/test_backtrace.rb
index 6ab9032..91dec4a 100644
--- a/test/ruby/test_backtrace.rb
+++ b/test/ruby/test_backtrace.rb
@@ -85,6 +85,10 @@ class TestBacktrace < Test::Unit::TestCase
     rec[m]
   end
 
+  def test_caller_with_nil_length
+    assert_equal caller(0), caller(0, nil)
+  end
+
   def test_caller_locations
     cs = caller(0); locs = caller_locations(0).map{|loc|
       loc.to_s
diff --git a/vm_backtrace.c b/vm_backtrace.c
index 3287c1f..3945993 100644
--- a/vm_backtrace.c
+++ b/vm_backtrace.c
@@ -787,6 +787,8 @@ vm_backtrace_to_ary(rb_thread_t *th, int argc, VALUE *argv, int lev_default, int
 
     rb_scan_args(argc, argv, "02", &level, &vn);
 
+    if (argc == 2 && NIL_P(vn)) argc--;
+
     switch (argc) {
       case 0:
 	lev = lev_default + lev_plus;