diff --git a/feeds_ui/feeds_ui.admin.inc b/feeds_ui/feeds_ui.admin.inc
index b9fe2a6..65b1615 100644
--- a/feeds_ui/feeds_ui.admin.inc
+++ b/feeds_ui/feeds_ui.admin.inc
@@ -401,6 +401,15 @@ function feeds_ui_edit_page(FeedsImporter $importer, $active = 'help', $plugin_k
   $info['actions'] = array(l(t('Change'), $path . '/processor'));
   $config_info[] = $info;
 
+  // Validate configuration.
+  $errors = $importer->validateConfig();
+  if (count($errors)) {
+    $message = t('There are some issues with the importer configuration: !errors', array(
+      '!errors' => theme('item_list', array('items' => $errors)),
+    ));
+    drupal_set_message($message, 'warning');
+  }
+
   return theme('feeds_ui_edit_page', array(
     'info' => $config_info,
     'active' => $active_container,
@@ -1207,12 +1216,21 @@ function feeds_ui_importer_import_validate($form, &$form_state) {
   }
 
   if (!$form_state['values']['bypass_validation']) {
+    $errors = array();
+
+    $importer = feeds_importer($feeds_importer->id);
+    $importer->setConfig($feeds_importer->config);
     foreach (array('fetcher', 'parser', 'processor') as $type) {
       $plugin = feeds_plugin($feeds_importer->config[$type]['plugin_key'], $feeds_importer->id);
-      if (get_class($plugin) == 'FeedsMissingPlugin') {
-        form_error($form['importer'], t('The plugin %plugin is unavailable.', array('%plugin' => $feeds_importer->config[$type]['plugin_key'])));
+      if (!($plugin instanceof FeedsMissingPlugin)) {
+        $importer->setPlugin($feeds_importer->config[$type]['plugin_key']);
+        $importer->$type->setConfig($feeds_importer->config[$type]['config']);
       }
     }
+    $errors = array_merge($errors, $importer->validateConfig());
+    if (!empty($errors)) {
+      form_error($form['importer'], theme('item_list', array('items' => $errors)));
+    }
   }
 
   $form_state['importer'] = $feeds_importer;
diff --git a/feeds_ui/feeds_ui.test b/feeds_ui/feeds_ui.test
index 7378b91..14694a4 100644
--- a/feeds_ui/feeds_ui.test
+++ b/feeds_ui/feeds_ui.test
@@ -18,7 +18,7 @@ class FeedsUIUserInterfaceTestCase extends FeedsWebTestCase {
   }
 
   public function setUp() {
-    parent::setUp(array('php'), array('use PHP for settings'));
+    parent::setUp(array('php', 'locale'), array('use PHP for settings', 'administer languages'));
   }
 
   /**
@@ -116,6 +116,85 @@ class FeedsUIUserInterfaceTestCase extends FeedsWebTestCase {
     // @todo Refreshing/deleting feed items. Needs to live in feeds.test
   }
 
+  /**
+   * Tests if the user is warned when an invalid plugin is used.
+   */
+  public function testInvalidPlugin() {
+    // Create an importer.
+    $this->createImporterConfiguration('Test feed', 'test_feed');
+
+    // Add invalid fetcher plugin.
+    $invalid_plugin = $this->randomName();
+    $importer = feeds_importer('test_feed');
+    $importer->addConfig(array(
+      'fetcher' => array(
+        'plugin_key' => $invalid_plugin,
+        'config' => array(),
+      ),
+    ));
+    $importer->save();
+
+    // Assert error message on importer page.
+    $this->drupalGet('admin/structure/feeds/test_feed');
+    $this->assertText(format_string('The plugin @invalid_plugin is unavailable.', array(
+      '@invalid_plugin' => $invalid_plugin,
+    )));
+  }
+
+  /**
+   * Tests if the user is warned when an invalid bundle is selected.
+   */
+  public function testInvalidBundle() {
+    // Create an importer.
+    $this->createImporterConfiguration('Test feed', 'test_feed');
+
+    // Set invalid bundle.
+    $invalid_bundle = drupal_strtolower($this->randomName());
+    $importer = feeds_importer('test_feed');
+    $importer->processor->addConfig(array(
+      'bundle' => $invalid_bundle,
+    ));
+    $importer->save();
+
+    // Assert error message on processor settings page.
+    $this->drupalGet('admin/structure/feeds/test_feed/settings/FeedsNodeProcessor');
+    $this->assertText(format_string('Invalid value @invalid_bundle for config option Bundle.', array(
+      '@invalid_bundle' => $invalid_bundle,
+    )));
+
+    // But the option should still be selected.
+    $this->assertFieldByName('bundle', $invalid_bundle);
+  }
+
+  /**
+   * Tests if the user is warned when an invalid language is selected.
+   */
+  public function testInvalidLanguage() {
+    // Add the Dutch language.
+    $edit = array(
+      'langcode' => 'nl',
+    );
+    $this->drupalPost('admin/config/regional/language/add', $edit, t('Add language'));
+
+    // Create an importer.
+    $this->createImporterConfiguration('Test feed', 'test_feed');
+    // Change processor's language to Dutch.
+    $this->setSettings('test_feed', 'FeedsNodeProcessor', array('language' => 'nl'));
+
+    // Now remove the Dutch language.
+    $path = 'admin/config/regional/language/delete/nl';
+    $this->drupalPost($path, array(), t('Delete'));
+
+    // Assert error message on processor settings page.
+    $this->drupalGet('admin/structure/feeds/test_feed/settings/FeedsNodeProcessor');
+    $this->assertText(format_string('Invalid value @invalid_lang for config option Language.', array(
+      '@invalid_lang' => 'nl',
+    )));
+
+    // But the option should still be selected.
+    $this->assertFieldByName('language', 'nl');
+  }
+
   public function testImporterImport() {
     $name = $this->randomString();
     $id = drupal_strtolower($this->randomName());
@@ -157,4 +236,71 @@ class FeedsUIUserInterfaceTestCase extends FeedsWebTestCase {
     $this->assertTrue($config['skip_hash_check']);
   }
 
+  /**
+   * Tests if the user is warned when importing an importer with invalid configuration.
+   */
+  public function testInvalidConfigurationWhenImportingImporter() {
+    $name = $this->randomString();
+    $id = drupal_strtolower($this->randomName());
+    $this->createImporterConfiguration($name, $id);
+    $this->setPlugin($id, 'FeedsCSVParser');
+    $this->setPlugin($id, 'FeedsFileFetcher');
+
+    $this->drupalGet('admin/structure/feeds/' . $id . '/export');
+
+    $export = $this->xpath('//textarea[1]/text()');
+    $export = (string) $export[0];
+
+    // Add in some invalid configuration in the export.
+    $invalid_plugin = $this->randomName();
+    $invalid_bundle = strtolower($this->randomName());
+    $invalid_language = 'de';
+    $export = str_replace('FeedsFileFetcher', $invalid_plugin, $export);
+    $export = str_replace("'bundle' => 'article'", "'bundle' => '" . $invalid_bundle . "'", $export);
+    $export = str_replace("'language' => 'und'", "'language' => '" . $invalid_language . "'", $export);
+
+    // Delete this importer.
+    $this->drupalPost('admin/structure/feeds/' . $id . '/delete', array(), t('Delete'));
+
+    // Try to import.
+    $edit = array(
+      'importer' => $export,
+    );
+    $this->drupalPost('admin/structure/feeds/import', $edit, t('Import'));
+
+    // Assert that the importer was not imported.
+    $this->assertNoText("Successfully imported the $id feeds importer.");
+    $this->assertFalse(feeds_importer_load($id), 'The importer was not created.');
+
+    // Assert error messages.
+    $this->assertText(format_string('The plugin @invalid_plugin is unavailable.', array(
+      '@invalid_plugin' => $invalid_plugin,
+    )));
+    $this->assertText(format_string('Invalid value @invalid_bundle for config option Bundle.', array(
+      '@invalid_bundle' => $invalid_bundle,
+    )));
+    $this->assertText(format_string('Invalid value @invalid_lang for config option Language.', array(
+      '@invalid_lang' => $invalid_language,
+    )));
+
+    // Try if the importer is imported when ignoring validation.
+    $edit['bypass_validation'] = 1;
+    $this->drupalPost(NULL, $edit, t('Import'));
+
+    // Assert that the importer has been imported now.
+    drupal_static_reset();
+    $this->assertTrue(feeds_importer_load($id) instanceof FeedsImporter, 'The importer was created.');
+
+    // But the warnings should still be displayed.
+    $this->drupalGet('admin/structure/feeds/' . $id);
+    $this->assertText(format_string('The plugin @invalid_plugin is unavailable.', array(
+      '@invalid_plugin' => $invalid_plugin,
+    )));
+    $this->assertText(format_string('Invalid value @invalid_bundle for config option Bundle.', array(
+      '@invalid_bundle' => $invalid_bundle,
+    )));
+    $this->assertText(format_string('Invalid value @invalid_lang for config option Language.', array(
+      '@invalid_lang' => $invalid_language,
+    )));
+  }
 }
diff --git a/includes/FeedsConfigurable.inc b/includes/FeedsConfigurable.inc
index 93ad2eb..6fb9f94 100644
--- a/includes/FeedsConfigurable.inc
+++ b/includes/FeedsConfigurable.inc
@@ -182,6 +182,16 @@ abstract class FeedsConfigurable {
   }
 
   /**
+   * Validates the configuration.
+   *
+   * @return array
+   *   A list of errors.
+   */
+  public function validateConfig() {
+    return array();
+  }
+
+  /**
    * Returns whether or not the configurable has a config form.
    *
    * @return bool
diff --git a/includes/FeedsImporter.inc b/includes/FeedsImporter.inc
index cad7695..0edf669 100644
--- a/includes/FeedsImporter.inc
+++ b/includes/FeedsImporter.inc
@@ -177,6 +177,38 @@ class FeedsImporter extends FeedsConfigurable {
   }
 
   /**
+   * Validates the configuration.
+   */
+  public function validateConfig() {
+    $errors = parent::validateConfig();
+
+    // Validate errors of each plugin as well.
+    $plugin_types = array(
+      'fetcher' => t('Fetcher'),
+      'parser' => t('Parser'),
+      'processor' => t('Processor'),
+    );
+    foreach ($plugin_types as $type => $plugin_label) {
+      // Check if plugin exists.
+      $plugin = feeds_plugin($this->config[$type]['plugin_key'], $this->id);
+      if ($plugin instanceof FeedsMissingPlugin) {
+        $errors[] = t('The plugin %plugin is unavailable.', array('%plugin' => $this->config[$type]['plugin_key']));
+        continue;
+      }
+
+      $plugin_errors = $this->$type->validateConfig();
+      foreach ($plugin_errors as $key => $error) {
+        $errors[] = t('@plugin: !error', array(
+          '@plugin' => $plugin_label,
+          '!error' => $error,
+        ));
+      }
+    }
+
+    return $errors;
+  }
+
+  /**
    * Return defaults for feed configuration.
    */
   public function configDefaults() {
diff --git a/plugins/FeedsPlugin.inc b/plugins/FeedsPlugin.inc
index 65115f8..6b44881 100644
--- a/plugins/FeedsPlugin.inc
+++ b/plugins/FeedsPlugin.inc
@@ -210,6 +210,12 @@ abstract class FeedsPlugin extends FeedsConfigurable implements FeedsSourceInter
   public static function child($plugin_key, $parent_plugin) {
     ctools_include('plugins');
     $plugins = ctools_get_plugins('feeds', 'plugins');
+
+    if (!isset($plugins[$plugin_key])) {
+      // Plugin is not available.
+      return FALSE;
+    }
+
     $info = $plugins[$plugin_key];
 
     if (empty($info['handler']['parent'])) {
diff --git a/plugins/FeedsProcessor.inc b/plugins/FeedsProcessor.inc
index 7898f24..687cffe 100644
--- a/plugins/FeedsProcessor.inc
+++ b/plugins/FeedsProcessor.inc
@@ -913,6 +913,42 @@ abstract class FeedsProcessor extends FeedsPlugin {
   }
 
   /**
+   * Validates the configuration.
+   *
+   * @return array
+   *   A list of errors.
+   */
+  public function validateConfig() {
+    $errors = parent::validateConfig();
+    $info = $this->entityInfo();
+    $config = $this->getConfig();
+
+    // Check configured bundle.
+    if (isset($config['bundle'])) {
+      $bundles = $this->bundleOptions();
+      if (!in_array($config['bundle'], array_keys($bundles))) {
+        $errors[] = t('Invalid value %value for config option %key.', array(
+          '%value' => $config['bundle'],
+          '%key' => !empty($info['bundle name']) ? $info['bundle name'] : t('Bundle'),
+        ));
+      }
+    }
+
+    // Check configured language.
+    if (module_exists('locale') && !empty($info['entity keys']['language']) && isset($config['language'])) {
+      $languages = array(LANGUAGE_NONE) + array_keys(locale_language_list('name'));
+      if (!in_array($config['language'], $languages)) {
+        $errors[] = t('Invalid value %value for config option %key.', array(
+          '%value' => $config['language'],
+          '%key' => t('Language'),
+        ));
+      }
+    }
+
+    return $errors;
+  }
+
+  /**
    * Overrides parent::configForm().
    */
   public function configForm(&$form_state) {
@@ -920,13 +956,21 @@ abstract class FeedsProcessor extends FeedsPlugin {
     $form = array();
 
     if (!empty($info['entity keys']['bundle'])) {
+      $default_bundle = $this->bundle();
       $form['bundle'] = array(
         '#type' => 'select',
         '#options' => $this->bundleOptions(),
         '#title' => !empty($info['bundle name']) ? $info['bundle name'] : t('Bundle'),
         '#required' => TRUE,
-        '#default_value' => $this->bundle(),
+        '#default_value' => $default_bundle,
       );
+
+      // Add default value as one of the options if not yet available.
+      if (!isset($form['bundle']['#options'][$default_bundle])) {
+        $form['bundle']['#options'][$default_bundle] = t('Unknown bundle: @bundle', array(
+          '@bundle' => $default_bundle,
+        ));
+      }
     }
     else {
       $form['bundle'] = array(
@@ -943,6 +987,13 @@ abstract class FeedsProcessor extends FeedsPlugin {
         '#required' => TRUE,
         '#default_value' => $this->config['language'],
       );
+
+      // Add default value as one of the options if not yet available.
+      if (!isset($form['language']['#options'][$this->config['language']])) {
+        $form['language']['#options'][$this->config['language']] = t('Unknown language: @language', array(
+          '@language' => $this->config['language'],
+        ));
+      }
     }
 
     $tokens = array('@entities' => strtolower($info['label plural']));