diff --git a/core/modules/migrate/config/schema/migrate.data_types.schema.yml b/core/modules/migrate/config/schema/migrate.data_types.schema.yml
index 5b95871..e1b0231 100644
--- a/core/modules/migrate/config/schema/migrate.data_types.schema.yml
+++ b/core/modules/migrate/config/schema/migrate.data_types.schema.yml
@@ -24,7 +24,7 @@ migrate_source:
 migrate_source_sql:
   type: migrate_source
   mapping:
-    idlist:
+    id_list:
       type: sequence
       label: 'Source IDs to be migrated'
     target:
diff --git a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
index 332769c..e99c560 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
@@ -139,6 +139,9 @@
 
   // @TODO, find out how to remove this.
   // @see https://www.drupal.org/node/2443617
+  /**
+   * @var \Drupal\migrate\MigrateExecutableInterface
+   */
   public $migrateExecutable;
 
   /**
@@ -194,8 +197,9 @@ protected function getModuleHandler() {
    */
   protected function getIdList() {
     if (!empty($this->configuration['id_list'])) {
-      if (count($this->getIds()) > 1) {
-        throw new \LogicException('Cannot filter on multi-value key.');
+      // @TODO: Add support for multiple IDs https://www.drupal.org/node/2529744
+      if (count($this->getIds()) != 1) {
+        throw new \LogicException('Source IDs can only be specified by a list if there is only one id.');
       }
       return $this->configuration['id_list'];
     }
@@ -238,7 +242,7 @@ public function prepareRow(Row $row) {
   /**
    * Returns the iterator that will yield the row arrays to be processed.
    *
-   * @return \Iterator
+   * @return \Iterator|\Countable
    */
   public function getIterator() {
     if (!isset($this->iterator)) {
diff --git a/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
index 68700dc..cd8f606 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SqlBase.php
@@ -131,7 +131,7 @@ protected function initializeIterator() {
     $this->prepareQuery();
     $high_water_property = $this->migration->get('highWaterProperty');
 
-    if (empty($this->configuration['idlist'])) {
+    if (!$this->getIdList()) {
       // 1. If the map is joinable, join it. We will want to accept all rows
       //    which are either not in the map, or marked in the map as NEEDS_UPDATE.
       //    Note that if high water fields are in play, we want to accept all rows
diff --git a/core/modules/migrate/tests/src/Unit/MigrateSourceTest.php b/core/modules/migrate/tests/src/Unit/MigrateSourceTest.php
index d6e726a..6b73c66 100644
--- a/core/modules/migrate/tests/src/Unit/MigrateSourceTest.php
+++ b/core/modules/migrate/tests/src/Unit/MigrateSourceTest.php
@@ -93,7 +93,7 @@ protected function getSource($configuration = [], $migrate_config = [], $status
     $source_plugin
       ->expects($this->any())
       ->method('getIds')
-      ->willReturn([]);
+      ->willReturn(['test_sourceid1' => []]);
     $source_plugin
       ->expects($this->any())
       ->method('__toString')
@@ -172,7 +172,8 @@ public function testPrepareRowFalse() {
    * Test that the when a source id is in the idList, we don't get a row.
    */
   public function testIdInList() {
-    $source = $this->getSource([], ['idlist' => ['test_sourceid1']]);
+    $source = $this->getSource(['id_list' => ['test_sourceid1']]);
+
     $source->rewind();
 
     $this->assertNull($source->current(), 'No row is available because id was in idList.');
diff --git a/core/modules/migrate_drupal/tests/src/Unit/source/d6/NodeIdListTest.php b/core/modules/migrate_drupal/tests/src/Unit/source/d6/NodeIdListTest.php
index 4e2afcb..b01e0cb 100644
--- a/core/modules/migrate_drupal/tests/src/Unit/source/d6/NodeIdListTest.php
+++ b/core/modules/migrate_drupal/tests/src/Unit/source/d6/NodeIdListTest.php
@@ -15,14 +15,14 @@
 class NodeIdListTest extends NodeTest {
 
   // The fake Migration configuration entity.
-  protected $migrationConfiguration = array(
+  protected $migrationConfiguration = [
     'id' => 'test',
     // The fake configuration for the source.
-    'source' => array(
+    'source' => [
       'plugin' => 'd6_node',
       'id_list' => [1],
-    ),
-  );
+    ],
+  ];
 
   /**
    * {@inheritdoc}