diff -u b/src/Plugin/ConfigFilter/CollectionIgnore.php b/src/Plugin/ConfigFilter/CollectionIgnore.php
--- b/src/Plugin/ConfigFilter/CollectionIgnore.php
+++ b/src/Plugin/ConfigFilter/CollectionIgnore.php
@@ -20,7 +20,7 @@
  */
 class CollectionIgnore extends ConfigFilterBase implements ContainerFactoryPluginInterface {
 
-  private const FORCE_EXCLUSION_PREFIX = '~';
+  const FORCE_EXCLUSION_PREFIX = '~';
 
   /**
    * The active configuration storage.