diff -u b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTest.php
--- b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTest.php
@@ -248,2 +248,42 @@
 
+  /**
+   * Test configuration value data type enforcement using schemas.
+   */
+  protected function testConfigSaveWithSchema () {
+    $untyped_values = array(
+      'string' => 1,
+      'integer' => '100',
+      'boolean' => 1,
+      // In the config schema this does not have a type so should cast to string.
+      'no_type' => 1,
+      'array' => array(
+        'string' => 1
+      ),
+      // Not in schema and therefore should be left untouched.
+      'not_present_in_schema' => TRUE,
+    );
+
+    $typed_values = array(
+      'string' => '1',
+      'integer' => 100,
+      'boolean' => TRUE,
+      'no_type' => '1',
+      'array' => array(
+        'string' => '1'
+      ),
+      'not_present_in_schema' => TRUE,
+    );
+
+    // Save config which has a schema that enforces types.
+    \Drupal::config('config_test.schema_data_types')
+      ->setData($untyped_values)
+      ->save();
+    $this->assertIdentical(\Drupal::config('config_test.schema_data_types')->get(), $typed_values);
+
+    // Save config which does not have a schema that enforces types.
+    \Drupal::config('config_test.no_schema_data_types')
+           ->setData($untyped_values)
+           ->save();
+    $this->assertIdentical(\Drupal::config('config_test.no_schema_data_types')->get(), $untyped_values);
+  }
 }
only in patch2:
unchanged:
--- a/core/modules/config/tests/config_test/config/schema/config_test.schema.yml
+++ b/core/modules/config/tests/config_test/config/schema/config_test.schema.yml
@@ -91,3 +91,21 @@ config_test.dynamic.*:
     protected_property:
       type: string
       label: 'Protected property'
+
+config_test.schema_data_types:
+  type: mapping
+  label: 'Config test schema'
+  mapping:
+    integer:
+      type: integer
+    string:
+      type: string
+    boolean:
+      type: boolean
+    no_type:
+      label: 'No label'
+    array:
+      type: mapping
+      mapping:
+        string:
+          type: string
\ No newline at end of file