diff --git a/lib/jsonschema.rb b/lib/jsonschema.rb
index 5ee800d..e49dcef 100644
--- a/lib/jsonschema.rb
+++ b/lib/jsonschema.rb
@@ -45,8 +45,8 @@ def check_property value, schema, key, parent
         end
 
         if value == Undefined
-          unless schema['optional']
-            raise ValueError, "#{key_path}: is missing and it is not optional"
+          if schema['required']
+            raise ValueError, "#{key_path}: is missing and it is required"
           end
 
           # default
@@ -78,7 +78,7 @@ def check_property value, schema, key, parent
               if schema['items']
                 if schema['items'].kind_of?(Array)
                   schema['items'].each_with_index {|val, index|
-                    check_property(undefined_check(value, index), schema['items'][index], index, value)
+                    check_property(undefined_check(value, index), schema['items'][index].merge("required" => true), index, value)
                   }
                   if schema.include?('additionalProperties')
                     additional = schema['additionalProperties']
diff --git a/test/jsonschema_test.rb b/test/jsonschema_test.rb
index 01339ae..9e0f8d5 100644
--- a/test/jsonschema_test.rb
+++ b/test/jsonschema_test.rb
@@ -14,7 +14,6 @@ def test_self_schema
               "age" => {
                   "type"=> "integer",
                   "maximum"=> 125,
-                  "optional"=> true
               }
           }
       },
@@ -34,7 +33,6 @@ def test_self_schema
               "age" => {
                   "type"=> "integer",
                   "maximum"=> 125,
-                  "optional"=> true
               }
           }
       },
@@ -54,7 +52,6 @@ def test_self_schema
               "age" => {
                   "type"=> "integer",
                   "maximum"=> 125,
-                  "optional"=> true
               }
           }
       },
@@ -421,7 +418,7 @@ def test_properties
         },
         "prop02"=>{
           "type"=>"number",
-          "optional"=>true
+          "required"=>false
         },
         "prop03"=>{
           "type"=>"integer",
@@ -431,14 +428,14 @@ def test_properties
         },
         "prop05"=>{
           "type"=>"object",
-          "optional"=>true,
+          "required"=>false,
           "properties"=>{
             "subprop01"=>{
               "type"=>"string",
             },
             "subprop02"=>{
               "type"=>"string",
-              "optional"=>false
+              "required"=>true
             }
           }
         }
@@ -499,11 +496,9 @@ def test_requires
       "properties"=>{
         "prop01"=>{
           "type"=>"string",
-          "optional"=>true
         },
         "prop02"=>{
           "type"=>"number",
-          "optional"=>true,
           "requires"=>"prop01"
         }
       }
@@ -545,7 +540,7 @@ def test_pattern
     }
   end
 
-  def test_optional
+  def test_required
     schema = {
       "type"=>"object",
       "properties"=>{
@@ -554,14 +549,14 @@ def test_optional
         },
         "prop02"=>{
           "type"=>"number",
-          "optional"=>true
+          "required"=>false
         },
         "prop03"=>{
           "type"=>"integer"
         },
         "prop04"=>{
           "type"=>"boolean",
-          "optional"=>false
+          "required"=>true
         }
       }
     }
@@ -598,7 +593,6 @@ def test_default
     schema1 = {
       "properties"=>{
         "test"=>{
-          "optional"=>true,
           "default"=>10
         },
       }
@@ -606,7 +600,6 @@ def test_default
     schema2 = {
       "properties"=>{
         "test"=>{
-          "optional"=>true,
           "default"=>10,
           "readonly"=>true
         }