diff --git a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
index fb330718d0..da4d3b4ec7 100644
--- a/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
+++ b/core/modules/migrate/src/Plugin/migrate/source/SourcePluginBase.php
@@ -33,8 +33,8 @@
  *     \Drupal\migrate\Plugin\MigrateIdMapInterface::setUpdate()
  *     methods.
  * - The row is above the highwater mark.
- *   - The current value of the high_water_property set on the source plugin is
- *     used as a highwater mark.
+ *   - The highwater mark is the highest encountered value of the property
+ *     defined by the configuration key high_water_property.
  * - The source row has changed.
  *   - A row is considered changed only if the track_changes property is set on
  *     the source plugin and the source values for the row have changed since