diff --git a/ChangeLog b/ChangeLog
index 1233302d68..17d2aedbdc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Dec 27 11:47:46 2015  Kuniaki IGARASHI  <igaiga@gmail.com>
+
+	* test/ruby/test_string.rb (test_insert): The test cases are
+	  written in string.c comments as a reference.  [Fix GH-1173]
+
 Sun Dec 27 11:03:33 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* parse.y (show_bitstack): trace stack_type value if yydebug.
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 47bd0d56af..f907a28f99 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -956,6 +956,14 @@ class TestString < Test::Unit::TestCase
     assert_nil($~)
   end
 
+  def test_insert
+    assert_equal("Xabcd", S("abcd").insert(0, 'X'))
+    assert_equal("abcXd", S("abcd").insert(3, 'X'))
+    assert_equal("abcdX", S("abcd").insert(4, 'X'))
+    assert_equal("abXcd", S("abcd").insert(-3, 'X'))
+    assert_equal("abcdX", S("abcd").insert(-1, 'X'))
+  end
+
   def test_intern
     assert_equal(:koala, S("koala").intern)
     assert_not_equal(:koala, S("Koala").intern)