diff --git a/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
index bdeeba1..b3b51c2 100644
--- a/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -110,7 +110,7 @@ public function get($key = '') {
    * {@inheritdoc}
    */
   public function setData(array $data) {
-    $this->data = $data;
+    parent::setData($data);
     $this->resetOverriddenData();
     return $this;
   }
diff --git a/core/lib/Drupal/Core/Config/ConfigBase.php b/core/lib/Drupal/Core/Config/ConfigBase.php
index 3508611..37e0d80 100644
--- a/core/lib/Drupal/Core/Config/ConfigBase.php
+++ b/core/lib/Drupal/Core/Config/ConfigBase.php
@@ -160,13 +160,39 @@ public function get($key = '') {
    *
    * @return $this
    *   The configuration object.
+   *
+   * @throws \Drupal\Core\Config\ConfigValueException
+   *   If any key in $data in any depth contains a dot.
    */
   public function setData(array $data) {
+    $this->validateKeys($data);
     $this->data = $data;
     return $this;
   }
 
   /**
+   * Validate all keys in a passed in config array structure.
+   *
+   * @param array $data
+   *   Configuration array structure.
+   *
+   * @return null
+   *
+   * @throws \Drupal\Core\Config\ConfigValueException
+   *   If any key in $data in any depth contains a dot.
+   */
+  protected function validateKeys(array $data) {
+    foreach ($data as $key => $value) {
+      if (strpos($key, '.') !== FALSE) {
+        throw new ConfigValueException(String::format('@key key contains a dot which is not supported.', array('@key' => $key)));
+      }
+      if (is_array($value)) {
+        $this->validateKeys($value);
+      }
+    }
+  }
+
+  /**
    * Sets a value in this configuration object.
    *
    * @param string $key
@@ -176,10 +202,16 @@ public function setData(array $data) {
    *
    * @return $this
    *   The configuration object.
+   *
+   * @throws \Drupal\Core\Config\ConfigValueException
+   *   If $value is an array and any of its keys in any depth contains a dot.
    */
   public function set($key, $value) {
     // The dot/period is a reserved character; it may appear between keys, but
     // not within keys.
+    if (is_array($value)) {
+      $this->validateKeys($value);
+    }
     $parts = explode('.', $key);
     if (count($parts) == 1) {
       $this->data[$key] = $value;
diff --git a/core/lib/Drupal/Core/Config/ConfigValueException.php b/core/lib/Drupal/Core/Config/ConfigValueException.php
new file mode 100644
index 0000000..9802228
--- /dev/null
+++ b/core/lib/Drupal/Core/Config/ConfigValueException.php
@@ -0,0 +1,13 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Config\ConfigValueException.
+ */
+
+namespace Drupal\Core\Config;
+
+/**
+ * Exception thrown when config object values are invalid.
+ */
+class ConfigValueException extends ConfigException {}
diff --git a/core/modules/config/src/Tests/ConfigCRUDTest.php b/core/modules/config/src/Tests/ConfigCRUDTest.php
index 122843e..c38d3f6 100644
--- a/core/modules/config/src/Tests/ConfigCRUDTest.php
+++ b/core/modules/config/src/Tests/ConfigCRUDTest.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Core\Config\ConfigNameException;
+use Drupal\Core\Config\ConfigValueException;
 use Drupal\Core\Config\InstallStorage;
 use Drupal\simpletest\DrupalUnitTestBase;
 use Drupal\Core\Config\FileStorage;
@@ -184,6 +185,31 @@ function testNameValidation() {
   }
 
   /**
+   * Tests the validation of configuration object values.
+   */
+  function testValueValidation() {
+    // Verify that setData() will catch dotted keys.
+    $message = 'Expected ConfigValueException was thrown from setData() for value with dotted keys.';
+    try {
+      \Drupal::config('namespace.object')->setData(array('key.value' => 12))->save();
+      $this->fail($message);
+    }
+    catch (ConfigValueException $e) {
+      $this->pass($message);
+    }
+
+    // Verify that set() will catch dotted keys.
+    $message = 'Expected ConfigValueException was thrown from set() for value with dotted keys.';
+    try {
+      \Drupal::config('namespace.object')->set('foo', array('key.value' => 12))->save();
+      $this->fail($message);
+    }
+    catch (ConfigValueException $e) {
+      $this->pass($message);
+    }
+  }
+
+  /**
    * Tests data type handling.
    */
   public function testDataTypes() {
diff --git a/core/modules/options/src/Tests/OptionsFieldUITest.php b/core/modules/options/src/Tests/OptionsFieldUITest.php
index c69e797..0eac490 100644
--- a/core/modules/options/src/Tests/OptionsFieldUITest.php
+++ b/core/modules/options/src/Tests/OptionsFieldUITest.php
@@ -94,6 +94,11 @@ function testOptionsAllowedValuesInteger() {
     $string = "0|Zero";
     $array = array('0' => 'Zero');
     $this->assertAllowedValuesInput($string, $array, 'Values not in use can be removed.');
+
+    // Check that the same key can only be used once.
+    $string = "0|Zero\n0|One";
+    $array = array('0' => 'One');
+    $this->assertAllowedValuesInput($string, $array, 'Same value cannot be used multiple times.');
   }
 
   /**
@@ -144,6 +149,16 @@ function testOptionsAllowedValuesFloat() {
     $string = "0|Zero";
     $array = array('0' => 'Zero');
     $this->assertAllowedValuesInput($string, $array, 'Values not in use can be removed.');
+
+    // Check that the same key can only be used once.
+    $string = "0.5|Point five\n0.5|Half";
+    $array = array('0.5' => 'Half');
+    $this->assertAllowedValuesInput($string, $array, 'Same value cannot be used multiple times.');
+
+    // Check that different forms of the same float value cannot be used.
+    $string = "0|Zero\n.5|Point five\n0.5|Half";
+    $array = array('0' => 'Zero', '0.5' => 'Half');
+    $this->assertAllowedValuesInput($string, $array, 'Different forms of the same value cannot be used.');
   }
 
   /**
@@ -199,6 +214,16 @@ function testOptionsAllowedValuesText() {
     $string = "Zero";
     $array = array('Zero' => 'Zero');
     $this->assertAllowedValuesInput($string, $array, 'Values not in use can be removed.');
+
+    // Check that string values with dots can be used.
+    $string = "Zero\nexample.com|Example";
+    $array = array('Zero' => 'Zero', 'example.com' => 'Example');
+    $this->assertAllowedValuesInput($string, $array, 'String value with dot is supported.');
+
+    // Check that the same key can only be used once.
+    $string = "zero|Zero\nzero|One";
+    $array = array('zero' => 'One');
+    $this->assertAllowedValuesInput($string, $array, 'Same value cannot be used multiple times.');
   }
 
   /**