diff --git a/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
index 02afbd1..8263fd1 100644
--- a/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -208,13 +208,6 @@ public function isNew() {
    *   would return array('bar' => 'baz').
    *   If no key is specified, then the entire data array is returned.
    *
-   * The configuration system does not retain data types. Every saved value is
-   * casted to a string. In most cases this is not an issue; however, it can
-   * cause issues with Booleans, which are casted to "1" (TRUE) or "0" (FALSE).
-   * In particular, code relying on === or !== will no longer function properly.
-   *
-   * @see http://php.net/manual/language.operators.comparison.php
-   *
    * @return mixed
    *   The data that was requested.
    */
@@ -338,8 +331,6 @@ public function set($key, $value) {
     if (!$this->isLoaded) {
       $this->load();
     }
-    // Type-cast value into a string.
-    $value = $this->castValue($value);
 
     // The dot/period is a reserved character; it may appear between keys, but
     // not within keys.
@@ -355,46 +346,6 @@ public function set($key, $value) {
   }
 
   /**
-   * Casts a saved value to a string.
-   *
-   * The configuration system only saves strings or arrays. Any scalar
-   * non-string value is cast to a string. The one exception is boolean FALSE
-   * which would normally become '' when cast to a string, but is manually
-   * cast to '0' here for convenience and consistency.
-   *
-   * Any non-scalar value that is not an array (aka objects) gets cast
-   * to an array.
-   *
-   * @param mixed $value
-   *   A value being saved into the configuration system.
-   *
-   * @return string
-   *   The value cast to a string or array.
-   */
-  public function castValue($value) {
-    if (is_scalar($value) || $value === NULL) {
-      // Handle special case of FALSE, which should be '0' instead of ''.
-      if ($value === FALSE) {
-        $value = '0';
-      }
-      else {
-        $value = (string) $value;
-      }
-    }
-    else {
-      // Any non-scalar value must be an array.
-      if (!is_array($value)) {
-        $value = (array) $value;
-      }
-      // Recurse into any nested keys.
-      foreach ($value as $key => $nested_value) {
-        $value[$key] = $this->castValue($nested_value);
-      }
-    }
-    return $value;
-  }
-
-  /**
    * Unsets value in this config object.
    *
    * @param string $key
diff --git a/core/lib/Drupal/Core/Config/FileStorage.php b/core/lib/Drupal/Core/Config/FileStorage.php
index 6e428b3..24a6511 100644
--- a/core/lib/Drupal/Core/Config/FileStorage.php
+++ b/core/lib/Drupal/Core/Config/FileStorage.php
@@ -153,6 +153,7 @@ protected function getDumper() {
       // 2 spaces for consistency with Drupal coding standards.
       $this->dumper->setIndentation(2);
     }
+
     return $this->dumper;
   }
 
@@ -175,8 +176,9 @@ protected function getParser() {
    */
   public function encode($data) {
     // The level where you switch to inline YAML is set to PHP_INT_MAX to ensure
-    // this does not occur.
-    return $this->getDumper()->dump($data, PHP_INT_MAX);
+    // this does not occur. Also set the exceptionOnInvalidType parameter to
+    // TRUE, so exceptions are thrown for an invalid data type.
+    return $this->getDumper()->dump($data, PHP_INT_MAX, 0, TRUE);
   }
 
   /**
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
index 41b5f4d..7aff2a0 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
@@ -95,18 +95,18 @@ protected function createTests() {
     // Ensure that default values are filled in.
     $expected_properties = array(
       'id' => 'stark.test_block',
-      'weight' => '',
-      'status' => '1',
+      'weight' => NULL,
+      'status' => TRUE,
       'langcode' => language_default()->id,
-      'region' => '-1',
+      'region' => -1,
       'plugin' => 'test_html_id',
       'settings' => array(
-        'cache' => '1',
+        'cache' => 1,
         'label' => '',
         'module' => 'block_test',
         'label_display' => BlockInterface::BLOCK_LABEL_VISIBLE,
       ),
-      'visibility' => '',
+      'visibility' => NULL,
     );
     $this->assertIdentical($actual_properties, $expected_properties, 'The block properties are exported correctly.');
 
diff --git a/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorAdminTest.php b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorAdminTest.php
index 0419c4d..7fe5f28 100644
--- a/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorAdminTest.php
+++ b/core/modules/ckeditor/lib/Drupal/ckeditor/Tests/CKEditorAdminTest.php
@@ -164,10 +164,10 @@ function testAdmin() {
     $this->drupalGet('admin/config/content/formats/manage/filtered_html');
     $ultra_llama_mode_checkbox = $this->xpath('//input[@type="checkbox" and @name="editor[settings][plugins][llama_contextual_and_button][ultra_llama_mode]" and @checked="checked"]');
     $this->assertTrue(count($ultra_llama_mode_checkbox) === 1, 'The "Ultra llama mode" checkbox exists and is checked.');
-    $expected_settings['plugins']['llama_contextual_and_button']['ultra_llama_mode'] = '1';
+    $expected_settings['plugins']['llama_contextual_and_button']['ultra_llama_mode'] = 1;
     $editor = entity_load('editor', 'filtered_html');
     $this->assertTrue($editor instanceof Editor, 'An Editor config entity exists.');
-    $this->assertIdentical($expected_settings, $editor->settings, 'The Editor config entity has the correct settings.');
+    $this->assertIdentical($expected_settings, $editor->settings);
   }
 
 }
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigCRUDTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigCRUDTest.php
index d4c170c..195fba1 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigCRUDTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigCRUDTest.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Config\ConfigNameException;
 use Drupal\simpletest\DrupalUnitTestBase;
+use Drupal\Core\Config\FileStorage;
 
 /**
  * Tests CRUD operations on configuration objects.
@@ -131,7 +132,7 @@ function testCRUD() {
   /**
    * Tests the validation of configuration object names.
    */
-  function testNameValidation() {
+  public function testNameValidation() {
     // Verify that an object name without namespace causes an exception.
     $name = 'nonamespace';
     $message = 'Expected ConfigNameException was thrown for a name without a namespace.';
@@ -194,5 +195,56 @@ function testNameValidation() {
       $this->pass($message);
     }
   }
-}
 
+  /**
+   * Tests data type handling.
+   */
+  public function testDataTypes() {
+    $this->container->get('module_handler')->enable(array('config_test'));
+    $storage = new FileStorage($this->configDirectories[CONFIG_ACTIVE_DIRECTORY]);
+    $name = 'config_test.types';
+    $config = $this->container->get('config.factory')->get($name);
+    $original_content = file_get_contents($storage->getFilePath($name));
+    $this->verbose('<pre>' . $original_content . "\n" . var_export($storage->read($name), TRUE));
+
+    // Verify variable data types are intact.
+    $data = array(
+      'array' => array(),
+      'boolean' => TRUE,
+      'exp' => 1.2e+34,
+      'float' => 3.14159,
+      'hex' => 0xC,
+      'int' => 99,
+      'octal' => 0775,
+      'string' => 'string',
+      'string_int' => '1',
+    );
+    $this->assertIdentical($config->get(), $data);
+
+    // Re-set each key using Config::set().
+    foreach($data as $key => $value) {
+      $config->set($key, $value);
+    }
+    $config->save();
+    $this->assertIdentical($config->get(), $data);
+    // Assert the data against the file storage.
+    $this->assertIdentical($storage->read($name), $data);
+    $this->verbose('<pre>' . file_get_contents($storage->getFilePath($name)) . var_export($storage->read($name), TRUE));
+
+    // Set data using config::setData().
+    $config->setData($data)->save();
+    $this->assertIdentical($config->get(), $data);
+    $this->assertIdentical($storage->read($name), $data);
+
+    try {
+      $config->set('stream', fopen(__FILE__, 'r'))->save();
+      $this->fail('No Exception thrown upon saving invalid data type.');
+    }
+    catch (\Exception $e) {
+      $this->pass(format_string('%class thrown upon saving invalid data type.', array(
+        '%class' => get_class($e),
+      )));
+    }
+  }
+
+}
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
index faaccde..34b5943 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigEntityTest.php
@@ -150,8 +150,7 @@ function testCRUD() {
     // Verify that the entity was overwritten.
     $same_id = entity_load('config_test', $config_test->id());
     $this->assertIdentical($same_id->id(), $config_test->id());
-    // Note: Reloading loads from FileStorage, and FileStorage enforces strings.
-    $this->assertIdentical($same_id->label(), '');
+    $this->assertIdentical($same_id->label(), NULL);
     $this->assertNotEqual($same_id->uuid(), $config_test->uuid());
 
     // Delete the overridden entity first.
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigFileContentTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigFileContentTest.php
index f2e7965..7d4e43a 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigFileContentTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigFileContentTest.php
@@ -123,7 +123,7 @@ function testReadWriteConfig() {
     $this->assertEqual($config->get($true_key), '1', format_string("Boolean TRUE value returned the string '1'."));
 
     // Read null value.
-    $this->assertIdentical($config->get('null'), '');
+    $this->assertIdentical($config->get('null'), NULL);
 
     // Read false that had been nested in an array value
     $this->assertEqual($config->get($casting_array_false_value_key), '0', format_string("Nested boolean FALSE value returned the string '0'."));
diff --git a/core/modules/config/lib/Drupal/config/Tests/Storage/ConfigStorageTestBase.php b/core/modules/config/lib/Drupal/config/Tests/Storage/ConfigStorageTestBase.php
index a2b3448..d986835 100644
--- a/core/modules/config/lib/Drupal/config/Tests/Storage/ConfigStorageTestBase.php
+++ b/core/modules/config/lib/Drupal/config/Tests/Storage/ConfigStorageTestBase.php
@@ -161,6 +161,30 @@ function testCRUD() {
 
   }
 
+  /**
+   * Tests storage controller writing and reading data preserving data type.
+   */
+  function testDataTypes() {
+    $name = 'config_test.types';
+    $data = array(
+      'array' => array(),
+      'boolean' => TRUE,
+      'exp' => 1.2e+34,
+      'float' => 3.14159,
+      'hex' => 0xC,
+      'int' => 99,
+      'octal' => 0775,
+      'string' => 'string',
+      'string_int' => '1',
+    );
+
+    $result = $this->storage->write($name, $data);
+    $this->assertIdentical($result, TRUE);
+
+    $read_data = $this->storage->read($name);
+    $this->assertIdentical($read_data, $data);
+  }
+
   abstract protected function read($name);
 
   abstract protected function insert($name, $data);
diff --git a/core/modules/config/tests/config_test/config/config_test.types.yml b/core/modules/config/tests/config_test/config/config_test.types.yml
new file mode 100644
index 0000000..4ab2cdc
--- /dev/null
+++ b/core/modules/config/tests/config_test/config/config_test.types.yml
@@ -0,0 +1,9 @@
+array: []
+boolean: true
+exp: 1.2e+34
+float: 3.14159
+hex: 0xC
+int: 99
+octal: 0775
+string: string
+string_int: '1'
diff --git a/core/modules/image/image.module b/core/modules/image/image.module
index 053075d..59e223a 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -484,8 +484,12 @@ function image_field_entity_update(FieldInterface $field) {
   // The value of a managed_file element can be an array if #extended == TRUE.
   $fid_new = (isset($field->settings['default_image']['fids']) ? $field->settings['default_image']['fids'] : $field->settings['default_image']);
   $fid_old = (isset($prior_field->settings['default_image']['fids']) ? $prior_field->settings['default_image']['fids'] : $prior_field->settings['default_image']);
+  // Ensure sure that fid_new and old are arrays, because default_image might
+  // be the fallback value 0, see image_field_info().
+  $fid_old = (array) $fid_old;
+  $fid_new = (array) $fid_new;
 
-  $file_new = $fid_new ? file_load($fid_new) : FALSE;
+  $file_new = $fid_new ? file_load(reset($fid_new)) : FALSE;
 
   if ($fid_new != $fid_old) {
 
@@ -497,7 +501,7 @@ function image_field_entity_update(FieldInterface $field) {
     }
 
     // Is there an old file?
-    if ($fid_old && ($file_old = file_load($fid_old[0]))) {
+    if ($fid_old && ($file_old = file_load(reset($fid_old)))) {
       file_usage()->delete($file_old, 'image', 'default_image', $field->uuid);
     }
   }
diff --git a/core/modules/node/lib/Drupal/node/Tests/NodeFormButtonsTest.php b/core/modules/node/lib/Drupal/node/Tests/NodeFormButtonsTest.php
index b52d825..f80c8b9 100644
--- a/core/modules/node/lib/Drupal/node/Tests/NodeFormButtonsTest.php
+++ b/core/modules/node/lib/Drupal/node/Tests/NodeFormButtonsTest.php
@@ -109,7 +109,7 @@ function testNodeFormButtons() {
     // the initial order of buttons and/or status of the node when creating
     // a node.
     variable_set('node_options_article', array('promote'));
-    config('node.type.article')->set('settings.node.options.status', 0)->save();
+    config('node.type.article')->set('settings.node.options.status', false)->save();
 
     // Verify the buttons on a node add form for an administrator.
     $this->drupalLogin($this->admin_user);
diff --git a/core/modules/system/lib/Drupal/system/Tests/Module/ModuleEnableTest.php b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleEnableTest.php
index 7ff9f68..bc1b704 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Module/ModuleEnableTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Module/ModuleEnableTest.php
@@ -32,7 +32,7 @@ public static function getInfo() {
    */
   function testEnableUserTwice() {
     $this->container->get('module_handler')->enable(array('user'), FALSE);
-    $this->assertIdentical(config('system.module')->get('enabled.user'), '0');
+    $this->assertIdentical(config('system.module')->get('enabled.user'), 0);
   }
 
   /**