diff --git a/src/wp-includes/pluggable.php b/src/wp-includes/pluggable.php
index fc0356aedf..a166ab017a 100644
--- a/src/wp-includes/pluggable.php
+++ b/src/wp-includes/pluggable.php
@@ -1550,7 +1550,7 @@ function wp_notify_moderator($comment_id) {
 	$user = get_userdata( $post->post_author );
 	// Send to the administration and to the post author if the author can modify the comment.
 	$emails = array( get_option( 'admin_email' ) );
-	if ( user_can( $user->ID, 'edit_comment', $comment_id ) && ! empty( $user->user_email ) ) {
+	if ( $user && user_can( $user->ID, 'edit_comment', $comment_id ) && ! empty( $user->user_email ) ) {
 		if ( 0 !== strcasecmp( $user->user_email, get_option( 'admin_email' ) ) )
 			$emails[] = $user->user_email;
 	}
diff --git a/tests/phpunit/tests/comment.php b/tests/phpunit/tests/comment.php
index 854619572d..b12474ebfb 100644
--- a/tests/phpunit/tests/comment.php
+++ b/tests/phpunit/tests/comment.php
@@ -148,4 +148,19 @@ class Tests_Comment extends WP_UnitTestCase {
 			unset( $_SERVER['REMOTE_ADDR'] );
 		}
 	}
+
+	/**
+	 * @ticket 32566
+	 */
+	public function test_wp_notify_moderator_should_not_throw_notice_when_post_author_is_0() {
+		$p = $this->factory->post->create( array(
+			'post_author' => 0,
+		) );
+
+		$c = $this->factory->comment->create( array(
+			'comment_post_ID' => $p,
+		) );
+
+		$this->assertTrue( wp_notify_moderator( $c ) );
+	}
 }