diff --git a/package_manager/src/Event/PreOperationStageEvent.php b/package_manager/src/Event/PreOperationStageEvent.php
index 226af627bd11375683c37155f7e29f22f4dff102..3af2e1a5ad1d92a805569234992ebd4071a93ff2 100644
--- a/package_manager/src/Event/PreOperationStageEvent.php
+++ b/package_manager/src/Event/PreOperationStageEvent.php
@@ -38,6 +38,12 @@ abstract class PreOperationStageEvent extends StageEvent {
 
   /**
    * Adds error information to the event.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup[] $messages
+   *   The error messages.
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup|null $summary
+   *   (optional) The summary of error messages. Only required if there
+   *   is more than one message.
    */
   public function addError(array $messages, ?TranslatableMarkup $summary = NULL): void {
     $this->results[] = ValidationResult::createError($messages, $summary);
diff --git a/src/Event/ReadinessCheckEvent.php b/src/Event/ReadinessCheckEvent.php
index 6304816aa5614971a265e8feb043abcc71810105..466038a10606975108e370b24cf7841f6c69bf84 100644
--- a/src/Event/ReadinessCheckEvent.php
+++ b/src/Event/ReadinessCheckEvent.php
@@ -65,6 +65,12 @@ class ReadinessCheckEvent extends PreOperationStageEvent {
 
   /**
    * Adds warning information to the event.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup[] $messages
+   *   The warning messages.
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup|null $summary
+   *   (optional) The summary of warning messages. Required if there is more
+   *   than one message.
    */
   public function addWarning(array $messages, ?TranslatableMarkup $summary = NULL): void {
     $this->results[] = ValidationResult::createWarning($messages, $summary);