diff -u b/core/modules/system/system.api.php b/core/modules/system/system.api.php
--- b/core/modules/system/system.api.php
+++ b/core/modules/system/system.api.php
@@ -2303,8 +2303,8 @@
 /**
  * Alter MIME type mappings used to determine MIME type from a file extension.
  *
- * Called by \Drupal\Core\File\MimeType\ExtensionMimeTypeGuesser::guess(). It is
- * used to allow modules to add to or modify the default mapping from
+ * Invoked by \Drupal\Core\File\MimeType\ExtensionMimeTypeGuesser::guess(). It
+ * is used to allow modules to add to or modify the default mapping from
  * \Drupal\Core\File\MimeType\ExtensionMimeTypeGuesser::$defaultMapping.
  *
  * @param $mapping