diff -u b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
--- b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
@@ -125,8 +125,8 @@
   /**
    * A list of items that were migrated before the current migration task.
    *
-   * This will be compared with $this->currentlyMigratedItems to remove items not present
-   * in the incoming data if $this->deleteMissing is TRUE.
+   * This will be compared with $this->currentlyMigratedItems to remove items
+   * not present in the incoming data if $this->deleteMissing is TRUE.
    *
    * @var array
    */