diff --git a/ChangeLog b/ChangeLog
index 60f9dd762e..fca8af76dc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+Sat Sep  3 18:40:57 2011  CHIKANAGA Tomoyuki  <nagachika00@gmail.com>
+
+	* lib/thread.rb (SizedQueue#max=) raise ArgumentError if max is not
+	  positive number. patch by Masaki Matsushita.
+	  [ruby-dev:44449] [Bug #5259]
+
+	* test/thread/test_queue.rb (test_sized_queue_initialize,
+	  test_sized_queue_assign_max): add tests for it.
+
 Fri Sep  2 21:11:16 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* io.c (validate_enc_binmode, prep_stdio): default to text mode on
diff --git a/lib/thread.rb b/lib/thread.rb
index 09f2d58ecc..524db69a18 100644
--- a/lib/thread.rb
+++ b/lib/thread.rb
@@ -269,6 +269,7 @@ class SizedQueue < Queue
   # Sets the maximum size of the queue.
   #
   def max=(max)
+    raise ArgumentError, "queue size must be positive" unless max > 0
     diff = nil
     @mutex.synchronize {
       if max <= @max
diff --git a/test/thread/test_queue.rb b/test/thread/test_queue.rb
index b0ffe0866d..685b41a54f 100644
--- a/test/thread/test_queue.rb
+++ b/test/thread/test_queue.rb
@@ -35,4 +35,22 @@ class TestQueue < Test::Unit::TestCase
     assert_equal 0, from_workers.size
     assert_equal 0, to_workers.size
   end
+
+  def test_sized_queue_initialize
+    q = SizedQueue.new(1)
+    assert_equal 1, q.max
+    assert_raise(ArgumentError) { SizedQueue.new(0) }
+    assert_raise(ArgumentError) { SizedQueue.new(-1) }
+  end
+
+  def test_sized_queue_assign_max
+    q = SizedQueue.new(2)
+    assert_equal(2, q.max)
+    q.max = 1
+    assert_equal(1, q.max)
+    assert_raise(ArgumentError) { q.max = 0 }
+    assert_equal(1, q.max)
+    assert_raise(ArgumentError) { q.max = -1 }
+    assert_equal(1, q.max)
+  end
 end