diff --git a/ChangeLog b/ChangeLog
index 67ae0bff0e..a8d6391b8e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Aug 31 15:54:11 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* ext/json: Merge json gem v1.5.4 (3dab4c5a6a97fac03dac).
+
 Wed Aug 31 13:09:41 2011  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
 
 	* numeric.c (flo_round): Avoid overflow by optimizing for trivial
diff --git a/ext/json/generator/generator.c b/ext/json/generator/generator.c
index 9a90d5f182..9ad037cd40 100644
--- a/ext/json/generator/generator.c
+++ b/ext/json/generator/generator.c
@@ -1001,6 +1001,8 @@ static VALUE cState_generate(VALUE self, VALUE obj)
  * * *allow_nan*: true if NaN, Infinity, and -Infinity should be
  *   generated, otherwise an exception is thrown, if these values are
  *   encountered. This options defaults to false.
+ * * *quirks_mode*: Enables quirks_mode for parser, that is for example
+ *   generating single JSON values instead of documents is possible.
  */
 static VALUE cState_initialize(int argc, VALUE *argv, VALUE self)
 {
diff --git a/ext/json/lib/json/add/complex.rb b/ext/json/lib/json/add/complex.rb
new file mode 100644
index 0000000000..d7ebebf5f7
--- /dev/null
+++ b/ext/json/lib/json/add/complex.rb
@@ -0,0 +1,22 @@
+unless defined?(::JSON::JSON_LOADED) and ::JSON::JSON_LOADED
+  require 'json'
+end
+defined?(::Complex) or require 'complex'
+
+class Complex
+  def self.json_create(object)
+    Complex(object['r'], object['i'])
+  end
+
+  def as_json(*)
+    {
+      JSON.create_id => self.class.name,
+      'r'            => real,
+      'i'            => imag,
+    }
+  end
+
+  def to_json(*)
+    as_json.to_json
+  end
+end
diff --git a/ext/json/lib/json/add/core.rb b/ext/json/lib/json/add/core.rb
index 4624be22c2..1ae00d01a5 100644
--- a/ext/json/lib/json/add/core.rb
+++ b/ext/json/lib/json/add/core.rb
@@ -241,39 +241,3 @@ class Regexp
     as_json.to_json
   end
 end
-
-class Rational
-  def self.json_create(object)
-    Rational(object['n'], object['d'])
-  end
-
-  def as_json(*)
-    {
-      JSON.create_id => self.class.name,
-      'n'            => numerator,
-      'd'            => denominator,
-    }
-  end
-
-  def to_json(*)
-    as_json.to_json
-  end
-end
-
-class Complex
-  def self.json_create(object)
-    Complex(object['r'], object['i'])
-  end
-
-  def as_json(*)
-    {
-      JSON.create_id => self.class.name,
-      'r'            => real,
-      'i'            => imag,
-    }
-  end
-
-  def to_json(*)
-    as_json.to_json
-  end
-end
diff --git a/ext/json/lib/json/add/rational.rb b/ext/json/lib/json/add/rational.rb
new file mode 100644
index 0000000000..867cd92f05
--- /dev/null
+++ b/ext/json/lib/json/add/rational.rb
@@ -0,0 +1,22 @@
+unless defined?(::JSON::JSON_LOADED) and ::JSON::JSON_LOADED
+  require 'json'
+end
+defined?(::Rational) or require 'rational'
+
+class Rational
+  def self.json_create(object)
+    Rational(object['n'], object['d'])
+  end
+
+  def as_json(*)
+    {
+      JSON.create_id => self.class.name,
+      'n'            => numerator,
+      'd'            => denominator,
+    }
+  end
+
+  def to_json(*)
+    as_json.to_json
+  end
+end
diff --git a/ext/json/parser/parser.c b/ext/json/parser/parser.c
index 4ea663c721..d1d14c79ca 100644
--- a/ext/json/parser/parser.c
+++ b/ext/json/parser/parser.c
@@ -1618,6 +1618,9 @@ static VALUE convert_encoding(VALUE source)
  *   defaults to true.
  * * *object_class*: Defaults to Hash
  * * *array_class*: Defaults to Array
+ * * *quirks_mode*: Enables quirks_mode for parser, that is for example
+ *   parsing single JSON values instead of documents is possible.
+ *
  */
 static VALUE cParser_initialize(int argc, VALUE *argv, VALUE self)
 {
diff --git a/test/json/test_json_addition.rb b/test/json/test_json_addition.rb
index f28f228c22..6297578f1f 100755
--- a/test/json/test_json_addition.rb
+++ b/test/json/test_json_addition.rb
@@ -3,7 +3,7 @@
 
 require 'test/unit'
 require File.join(File.dirname(__FILE__), 'setup_variant')
-load 'json/add/core.rb'
+require 'json/add/core.rb'
 require 'date'
 
 class TC_JSONAddition < Test::Unit::TestCase