diff --git a/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/DedupeBase.php b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/DedupeBase.php
index 3ad5b99..ebc600d 100644
--- a/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/DedupeBase.php
+++ b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/DedupeBase.php
@@ -10,6 +10,8 @@
 use Drupal\migrate\ProcessPluginBase;
 use Drupal\migrate\MigrateExecutable;
 use Drupal\migrate\Row;
+use Drupal\migrate\MigrateException;
+use Drupal\Component\Utility\Unicode;
 
 /**
  * This abstract base contains the dedupe logic.
@@ -28,9 +30,27 @@ public function transform($value, MigrateExecutable $migrate_executable, Row $ro
     $i = 1;
     $postfix = isset($this->configuration['postfix']) ? $this->configuration['postfix'] : '';
     $new_value = $value;
+    $postfix_with_count = '';
     while ($this->exists($new_value)) {
-      $new_value = $value . $postfix . $i++;
+      $postfix_with_count = $postfix . $i++;
     }
+    $start = isset($this->configuration['start']) ? $this->configuration['start'] : 0;
+    if (!is_int($start)) {
+      throw new MigrateException('The start position configuration key should be an integer. Omit this key to capture from the beginning of the string.');
+    }
+    $length = isset($this->configuration['length']) ? $this->configuration['length'] : NULL;
+    if (!is_null($length)) {
+      if (!is_int($length)) {
+        throw new MigrateException('The character length configuration key should be an integer. Omit this key to capture the entire string.');
+      }
+      // Subtract postfix and count characters if it exceeds desired length.
+      if (Unicode::strlen($new_value . $postfix_with_count) > $length) {
+        $length -= Unicode::strlen($postfix_with_count);
+      }
+    }
+    // Use optional start or length to return a portion of deduplicated value.
+    $new_value = Unicode::substr($new_value, $start, $length);
+    $new_value .= $postfix_with_count;
     return $new_value;
   }
 
diff --git a/core/modules/migrate/tests/Drupal/migrate/Tests/process/DedupeEntityTest.php b/core/modules/migrate/tests/Drupal/migrate/Tests/process/DedupeEntityTest.php
index c7a2db5..e46ac7c 100644
--- a/core/modules/migrate/tests/Drupal/migrate/Tests/process/DedupeEntityTest.php
+++ b/core/modules/migrate/tests/Drupal/migrate/Tests/process/DedupeEntityTest.php
@@ -7,6 +7,7 @@
 namespace Drupal\migrate\Tests\process;
 
 use Drupal\migrate\Plugin\migrate\process\DedupeEntity;
+use Drupal\Component\Utility\Unicode;
 
 /**
  * Test the deduplication entity process plugin.
@@ -74,7 +75,7 @@ protected function setUp() {
    *
    * @dataProvider providerTestDedupe
    */
-  public function testDedupe($count, $postfix = '') {
+  public function testDedupe($count, $postfix = '', $start = NULL, $length = NULL) {
     $configuration = array(
       'entity_type' => 'test_entity_type',
       'field' => 'test_field',
@@ -82,10 +83,50 @@ public function testDedupe($count, $postfix = '') {
     if ($postfix) {
       $configuration['postfix'] = $postfix;
     }
+    $configuration['start'] = isset($start) ? $start : NULL;
+    $configuration['length'] = isset($length) ? $length : NULL;
     $plugin = new DedupeEntity($configuration, 'dedupe_entity', array(), $this->getMigration(), $this->entityQueryFactory);
     $this->entityQueryExpects($count);
-    $return = $plugin->transform('test', $this->migrateExecutable, $this->row, 'testproperty');
-    $this->assertSame($return, 'test' . ($count ? $postfix . $count : ''));
+    $value = $this->randomName(32);
+    $actual = $plugin->transform($value, $this->migrateExecutable, $this->row, 'testproperty');
+    $expected = $value;
+    $postfix_with_count = $count ? $postfix . $count : '';
+    if (!is_null($length) && Unicode::strlen($expected . $postfix_with_count) > $length) {
+      $length -= Unicode::strlen($postfix_with_count);
+    }
+    $expected = Unicode::substr($value, $start, $length);
+    $expected .= $postfix_with_count;
+    $this->assertSame($expected, $actual);
+  }
+
+  /**
+   * Tests that invalid start position throws an exception.
+   */
+  public function testDedupeEntityInvalidStart() {
+    $configuration = array(
+      'entity_type' => 'test_entity_type',
+      'field' => 'test_field',
+      'start' => 'foobar',
+    );
+    $plugin = new DedupeEntity($configuration, 'dedupe_entity', array(), $this->getMigration(), $this->entityQueryFactory);
+    $this->entityQueryExpects(0);
+    $this->setExpectedException('Drupal\migrate\MigrateException', 'The start position configuration key should be an integer. Omit this key to capture from the beginning of the string.');
+    $plugin->transform('test_start', $this->migrateExecutable, $this->row, 'testproperty');
+  }
+
+  /**
+   * Tests that invalid length option throws an exception.
+   */
+  public function testDedupeEntityInvalidLength() {
+    $configuration = array(
+      'entity_type' => 'test_entity_type',
+      'field' => 'test_field',
+      'length' => 'foobar',
+    );
+    $plugin = new DedupeEntity($configuration, 'dedupe_entity', array(), $this->getMigration(), $this->entityQueryFactory);
+    $this->entityQueryExpects(0);
+    $this->setExpectedException('Drupal\migrate\MigrateException', 'The character length configuration key should be an integer. Omit this key to capture the entire string.');
+    $plugin->transform('test_length', $this->migrateExecutable, $this->row, 'testproperty');
   }
 
   /**
@@ -93,18 +134,38 @@ public function testDedupe($count, $postfix = '') {
    */
   public function providerTestDedupe() {
     return array(
-      // Tests the entity deduplication plugin when there is no duplication
-      // and no postfix.
+      // Tests no duplication.
       array(0),
-      // Tests the entity deduplication plugin when there is duplication but
-      // no postfix.
+      // Tests no duplication and start position.
+      array(0, NULL, 10),
+      // Tests no duplication, start position, and length.
+      array(0, NULL, 5, 10),
+      // Tests no duplication and length.
+      array(0, NULL, NULL, 10),
+      // Tests duplication.
       array(3),
-      // Tests the entity deduplication plugin when there is no duplication
-      // but there is a postfix.
+      // Tests duplication and start position.
+      array(3, NULL, 10),
+      // Tests duplication, start position, and length.
+      array(3, NULL, 5, 10),
+      // Tests duplication and length.
+      array(3, NULL, NULL, 10),
+      // Tests no duplication and postfix.
       array(0, '_'),
-      // Tests the entity deduplication plugin when there is duplication and
-      // there is a postfix.
+      // Tests no duplication, postfix, and start position.
+      array(0, '_', 5),
+      // Tests no duplication, postfix, start position, and length.
+      array(0, '_', 5, 10),
+      // Tests no duplication, postfix, and length.
+      array(0, '_', NULL, 10),
+      // Tests duplication and postfix.
       array(2, '_'),
+      // Tests duplication, postfix, and start position.
+      array(2, '_', 5),
+      // Tests duplication, postfix, start position, and length.
+      array(2, '_', 5, 10),
+      // Tests duplication, postfix, and length.
+      array(2, '_', NULL, 10),
     );
   }
 
diff --git a/core/modules/migrate_drupal/config/install/migrate.migration.d6_block.yml b/core/modules/migrate_drupal/config/install/migrate.migration.d6_block.yml
index e4c269c..05bd07d 100644
--- a/core/modules/migrate_drupal/config/install/migrate.migration.d6_block.yml
+++ b/core/modules/migrate_drupal/config/install/migrate.migration.d6_block.yml
@@ -9,6 +9,7 @@ process:
     entity_type: block
     field: id
     postfix: _
+    length: 32
     source: module
   plugin:
     -
diff --git a/core/modules/migrate_drupal/config/install/migrate.migration.d6_contact_category.yml b/core/modules/migrate_drupal/config/install/migrate.migration.d6_contact_category.yml
index e73f6ad..e0ac378 100644
--- a/core/modules/migrate_drupal/config/install/migrate.migration.d6_contact_category.yml
+++ b/core/modules/migrate_drupal/config/install/migrate.migration.d6_contact_category.yml
@@ -11,6 +11,7 @@ process:
       plugin: dedupe_entity
       entity_type: user_role
       field: cid
+      length: 32
   label: category
   recipients: recipients
   reply: reply
diff --git a/core/modules/migrate_drupal/config/install/migrate.migration.d6_filter_format.yml b/core/modules/migrate_drupal/config/install/migrate.migration.d6_filter_format.yml
index 88d5c0d..1dc7dbc 100644
--- a/core/modules/migrate_drupal/config/install/migrate.migration.d6_filter_format.yml
+++ b/core/modules/migrate_drupal/config/install/migrate.migration.d6_filter_format.yml
@@ -11,6 +11,7 @@ process:
       plugin: dedupe_entity
       entity_type: filter_format
       field: format
+      length: 32
   name: name
   cache: cache
   filters:
diff --git a/core/modules/migrate_drupal/config/install/migrate.migration.d6_taxonomy_vocabulary.yml b/core/modules/migrate_drupal/config/install/migrate.migration.d6_taxonomy_vocabulary.yml
index d654323..68fd460 100644
--- a/core/modules/migrate_drupal/config/install/migrate.migration.d6_taxonomy_vocabulary.yml
+++ b/core/modules/migrate_drupal/config/install/migrate.migration.d6_taxonomy_vocabulary.yml
@@ -11,6 +11,7 @@ process:
       plugin: dedupe_entity
       entity_type: taxonomy_vocabulary
       field: vid
+      length: 32
   label: name
   name: name
   description: description
diff --git a/core/modules/migrate_drupal/config/install/migrate.migration.d6_user_role.yml b/core/modules/migrate_drupal/config/install/migrate.migration.d6_user_role.yml
index cabd3c0..111a9a7 100644
--- a/core/modules/migrate_drupal/config/install/migrate.migration.d6_user_role.yml
+++ b/core/modules/migrate_drupal/config/install/migrate.migration.d6_user_role.yml
@@ -11,6 +11,7 @@ process:
       plugin: dedupe_entity
       entity_type: user_role
       field: id
+      length: 32
     -
       plugin: user_update_8002
   label: name
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6ContactCategory.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6ContactCategory.php
index d9db247..6c9d31a 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6ContactCategory.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6ContactCategory.php
@@ -83,6 +83,14 @@ public function load() {
         'weight' => '1',
         'selected' => '1',
       ))
+      ->values(array(
+        'cid' => '3',
+        'category' => 'A category much longer than thirty two characters',
+        'recipients' => 'fortyninechars@example.com',
+        'reply' => '',
+        'weight' => '2',
+        'selected' => '0',
+      ))
       ->execute();
     $this->setModuleVersion('contact', '6001');
   }
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6TaxonomyVocabulary.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6TaxonomyVocabulary.php
index 70b2429..148d1cd 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6TaxonomyVocabulary.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6TaxonomyVocabulary.php
@@ -179,6 +179,22 @@ public function load() {
       'module' => 'taxonomy',
       'weight' => '6',
     ))
+    ->values(array(
+      // Skipping vid 4 here, since it is already in use by
+      // Drupal6VocabularyField::load() and throws an
+      // IntegrityConstraintViolationException during MigrateDrupal6Test.
+      'vid' => '5',
+      'name' => 'vocabulary name much longer than thirty two characters',
+      'description' => 'description of vocabulary name much longer than thirty two characters',
+      'help' => '',
+      'relations' => '1',
+      'hierarchy' => '3',
+      'multiple' => '1',
+      'required' => '0',
+      'tags' => '0',
+      'module' => 'taxonomy',
+      'weight' => '7',
+    ))
     ->execute();
     $this->setModuleVersion('taxonomy', 6001);
   }
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6UserRole.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6UserRole.php
index 4c91ed9..41f5abe 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6UserRole.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/Dump/Drupal6UserRole.php
@@ -117,7 +117,7 @@ public static function getData($table) {
         array('rid' => 2, 'name' => 'authenticated user'),
         array('rid' => 3, 'name' => 'migrate test role 1'),
         array('rid' => 4, 'name' => 'migrate test role 2'),
-        array('rid' => 5, 'name' => 'migrate test role 3'),
+        array('rid' => 5, 'name' => 'migrate test role 3 that is longer than thirty two characters'),
       ),
     );
 
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateContactCategoryTest.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateContactCategoryTest.php
index dec8ff3..e73c323 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateContactCategoryTest.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateContactCategoryTest.php
@@ -64,6 +64,12 @@ public function testContactCategory() {
     $this->assertEqual($contact_category->recipients, array('test@example.com'));
     $this->assertEqual($contact_category->reply, 'Thanks for contacting us, we will reply ASAP!');
     $this->assertEqual($contact_category->weight, 1);
+
+    $contact_category = entity_load('contact_category', 'a_category_much_longer_than_thir');
+    $this->assertEqual($contact_category->label, 'A category much longer than thirty two characters');
+    $this->assertEqual($contact_category->recipients, array('fortyninechars@example.com'));
+    $this->assertEqual($contact_category->reply, '');
+    $this->assertEqual($contact_category->weight, 2);
   }
 
 }
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateTaxonomyVocabularyTest.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateTaxonomyVocabularyTest.php
index 719cd86..c2f6aad 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateTaxonomyVocabularyTest.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateTaxonomyVocabularyTest.php
@@ -59,8 +59,13 @@ public function testTaxonomyVocabulary() {
       $this->assertEqual($vocabulary->name, "vocabulary $j (i=$i)");
       $this->assertEqual($vocabulary->description, "description of vocabulary $j (i=$i)");
       $this->assertEqual($vocabulary->hierarchy, $i);
-      $this->assertEqual($vocabulary->weight, 4   + $i);
+      $this->assertEqual($vocabulary->weight, 4 + $i);
     }
+    $vocabulary = entity_load('taxonomy_vocabulary', 'vocabulary_name_much_longer_than');
+    $this->assertEqual($vocabulary->name, 'vocabulary name much longer than thirty two characters');
+    $this->assertEqual($vocabulary->description, 'description of vocabulary name much longer than thirty two characters');
+    $this->assertEqual($vocabulary->hierarchy, 3);
+    $this->assertEqual($vocabulary->weight, 7);
   }
 
 }
diff --git a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateUserRoleTest.php b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateUserRoleTest.php
index dffb1d2..98183e8 100644
--- a/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateUserRoleTest.php
+++ b/core/modules/migrate_drupal/lib/Drupal/migrate_drupal/Tests/d6/MigrateUserRoleTest.php
@@ -100,6 +100,10 @@ public function testUserRole() {
     ));
     $this->assertEqual($migrate_test_role_2->id(), $rid);
     $this->assertEqual(array($rid), $migration->getIdMap()->lookupDestinationId(array(4)));
+    $rid = 'migrate_test_role_3_that_is_long';
+    $migrate_test_role_3 = entity_load('user_role', $rid);
+    $this->assertEqual($migrate_test_role_3->id(), $rid);
+    $this->assertEqual(array($rid), $migration->getIdMap()->lookupDestinationId(array(5)));
   }
 
 }