diff --git a/ChangeLog b/ChangeLog
index 4ebb106b4e..731831f75f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Apr 24 14:54:03 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/optparse.rb (OptionParser#to_a): String#to_a is no longer
+	  defined.  [ruby-dev:45568][Bug #6348]
+
 Tue Apr 24 12:46:50 2012  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
 
 	* hash.c, object.c, struct.c, lib/ostruct.rb: add to_h methods.
diff --git a/lib/optparse.rb b/lib/optparse.rb
index a448459d46..75c6b76bc6 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -1065,13 +1065,13 @@ XXX
   #
   # Returns option summary string.
   #
-  def help; summarize(banner.to_s.sub(/\n?\z/, "\n")) end
+  def help; summarize("#{banner}".sub(/\n?\z/, "\n")) end
   alias to_s help
 
   #
   # Returns option summary list.
   #
-  def to_a; summarize(banner.to_a.dup) end
+  def to_a; summarize([*banner]) end
 
   #
   # Checks if an argument is given twice, in which case an ArgumentError is
diff --git a/test/optparse/test_summary.rb b/test/optparse/test_summary.rb
index 0c67d7f0f9..bda3b49890 100644
--- a/test/optparse/test_summary.rb
+++ b/test/optparse/test_summary.rb
@@ -18,4 +18,21 @@ class TestOptionParser::SummaryTest < TestOptionParser
     assert_match(/description 2/, s[1])
     assert_match(/last-option/, s[-1])
   end
+
+  def test_banner
+    o = OptionParser.new("foo bar")
+    assert_equal("foo bar", o.banner)
+  end
+
+  def test_banner_from_progname
+    o = OptionParser.new
+    o.program_name = "foobar"
+    assert_equal("Usage: foobar [options]\n", o.help)
+  end
+
+  def test_summary
+    o = OptionParser.new("foo bar")
+    assert_equal("foo bar\n", o.to_s)
+    assert_equal(["foo bar"], o.to_a)
+  end
 end