diff --git a/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
index 2a8018dc0b..9ff231e7a4 100644
--- a/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
@@ -248,8 +248,18 @@ abstract class AbstractObjectNormalizer extends AbstractNormalizer
                 return;
             }
 
-            $builtinType = $type->getBuiltinType();
-            $class = $type->getClassName();
+            if ($type->isCollection() && null !== ($collectionValueType = $type->getCollectionValueType()) && Type::BUILTIN_TYPE_OBJECT === $collectionValueType->getBuiltinType()) {
+                $builtinType = Type::BUILTIN_TYPE_OBJECT;
+                $class = $collectionValueType->getClassName().'[]';
+
+                if (null !== $collectionKeyType = $type->getCollectionKeyType()) {
+                    $context['key_type'] = $collectionKeyType;
+                }
+            } else {
+                $builtinType = $type->getBuiltinType();
+                $class = $type->getClassName();
+            }
+
             $expectedTypes[Type::BUILTIN_TYPE_OBJECT === $builtinType && $class ? $class : $builtinType] = true;
 
             if (Type::BUILTIN_TYPE_OBJECT === $builtinType) {
diff --git a/src/Symfony/Component/Serializer/Normalizer/ArrayDenormalizer.php b/src/Symfony/Component/Serializer/Normalizer/ArrayDenormalizer.php
index 921e312bd0..7d3d87c510 100644
--- a/src/Symfony/Component/Serializer/Normalizer/ArrayDenormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/ArrayDenormalizer.php
@@ -13,6 +13,7 @@ namespace Symfony\Component\Serializer\Normalizer;
 
 use Symfony\Component\Serializer\Exception\BadMethodCallException;
 use Symfony\Component\Serializer\Exception\InvalidArgumentException;
+use Symfony\Component\Serializer\Exception\UnexpectedValueException;
 use Symfony\Component\Serializer\SerializerAwareInterface;
 use Symfony\Component\Serializer\SerializerInterface;
 
@@ -30,6 +31,8 @@ class ArrayDenormalizer implements DenormalizerInterface, SerializerAwareInterfa
 
     /**
      * {@inheritdoc}
+     *
+     * @throws UnexpectedValueException
      */
     public function denormalize($data, $class, $format = null, array $context = array())
     {
@@ -46,12 +49,16 @@ class ArrayDenormalizer implements DenormalizerInterface, SerializerAwareInterfa
         $serializer = $this->serializer;
         $class = substr($class, 0, -2);
 
-        return array_map(
-            function ($data) use ($serializer, $class, $format, $context) {
-                return $serializer->denormalize($data, $class, $format, $context);
-            },
-            $data
-        );
+        $builtinType = isset($context['key_type']) ? $context['key_type']->getBuiltinType() : null;
+        foreach ($data as $key => $value) {
+            if (null !== $builtinType && !call_user_func('is_'.$builtinType, $key)) {
+                throw new UnexpectedValueException(sprintf('The type of the key "%s" must be "%s" ("%s" given).', $key, $builtinType, gettype($key)));
+            }
+
+            $data[$key] = $serializer->denormalize($value, $class, $format, $context);
+        }
+
+        return $data;
     }
 
     /**
diff --git a/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php b/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
index 8a09e516cd..ca1c4e0f59 100644
--- a/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
@@ -12,9 +12,12 @@
 namespace Symfony\Component\Serializer\Tests\Normalizer;
 
 use Doctrine\Common\Annotations\AnnotationReader;
+use Symfony\Component\PropertyInfo\Extractor\PhpDocExtractor;
 use Symfony\Component\PropertyInfo\Extractor\ReflectionExtractor;
+use Symfony\Component\PropertyInfo\PropertyInfoExtractor;
 use Symfony\Component\Serializer\Exception\UnexpectedValueException;
 use Symfony\Component\Serializer\NameConverter\CamelCaseToSnakeCaseNameConverter;
+use Symfony\Component\Serializer\Normalizer\ArrayDenormalizer;
 use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;
 use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
 use Symfony\Component\Serializer\Serializer;
@@ -525,13 +528,21 @@ class ObjectNormalizerTest extends \PHPUnit_Framework_TestCase
 
     public function testDenomalizeRecursive()
     {
-        $normalizer = new ObjectNormalizer(null, null, null, new ReflectionExtractor());
-        $serializer = new Serializer(array(new DateTimeNormalizer(), $normalizer));
+        $extractor = new PropertyInfoExtractor(array(), array(new PhpDocExtractor(), new ReflectionExtractor()));
+        $normalizer = new ObjectNormalizer(null, null, null, $extractor);
+        $serializer = new Serializer(array(new ArrayDenormalizer(), new DateTimeNormalizer(), $normalizer));
+
+        $obj = $serializer->denormalize(array(
+            'inner' => array('foo' => 'foo', 'bar' => 'bar'),
+            'date' => '1988/01/21',
+            'inners' => array(array('foo' => 1), array('foo' => 2)),
+        ), ObjectOuter::class);
 
-        $obj = $serializer->denormalize(array('inner' => array('foo' => 'foo', 'bar' => 'bar'), 'date' => '1988/01/21'), ObjectOuter::class);
         $this->assertEquals('foo', $obj->getInner()->foo);
         $this->assertEquals('bar', $obj->getInner()->bar);
         $this->assertEquals('1988-01-21', $obj->getDate()->format('Y-m-d'));
+        $this->assertEquals(1, $obj->getInners()[0]->foo);
+        $this->assertEquals(2, $obj->getInners()[1]->foo);
     }
 
     /**
@@ -546,6 +557,19 @@ class ObjectNormalizerTest extends \PHPUnit_Framework_TestCase
         $serializer->denormalize(array('date' => 'foo'), ObjectOuter::class);
     }
 
+    /**
+     * @expectedException UnexpectedValueException
+     * @expectedExceptionMessage The type of the key "a" must be "int" ("string" given).
+     */
+    public function testRejectInvalidKey()
+    {
+        $extractor = new PropertyInfoExtractor(array(), array(new PhpDocExtractor(), new ReflectionExtractor()));
+        $normalizer = new ObjectNormalizer(null, null, null, $extractor);
+        $serializer = new Serializer(array(new ArrayDenormalizer(), new DateTimeNormalizer(), $normalizer));
+
+        $serializer->denormalize(array('inners' => array('a' => array('foo' => 1))), ObjectOuter::class);
+    }
+
     public function testExtractAttributesRespectsFormat()
     {
         $normalizer = new FormatAndContextAwareNormalizer();
@@ -740,6 +764,11 @@ class ObjectOuter
     private $inner;
     private $date;
 
+    /**
+     * @var ObjectInner[]
+     */
+    private $inners;
+
     public function getInner()
     {
         return $this->inner;
@@ -759,6 +788,16 @@ class ObjectOuter
     {
         return $this->date;
     }
+
+    public function setInners(array $inners)
+    {
+        $this->inners = $inners;
+    }
+
+    public function getInners()
+    {
+        return $this->inners;
+    }
 }
 
 class ObjectInner
diff --git a/src/Symfony/Component/Serializer/composer.json b/src/Symfony/Component/Serializer/composer.json
index 29d40aab02..01fc76bab5 100644
--- a/src/Symfony/Component/Serializer/composer.json
+++ b/src/Symfony/Component/Serializer/composer.json
@@ -24,9 +24,10 @@
         "symfony/property-access": "~2.8|~3.0",
         "symfony/http-foundation": "~2.8|~3.0",
         "symfony/cache": "~3.1",
-        "symfony/property-info": "~2.8|~3.0",
+        "symfony/property-info": "~3.1",
         "doctrine/annotations": "~1.0",
-        "doctrine/cache": "~1.0"
+        "doctrine/cache": "~1.0",
+        "phpdocumentor/reflection-docblock": "~3.0"
     },
     "conflict": {
         "symfony/property-access": ">=3.0,<3.0.4|>=2.8,<2.8.4"