diff --git a/wp-includes/version.php b/wp-includes/version.php
index 6aa64cc5f0..ec211019a9 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.7-beta3-59254';
+$wp_version = '6.7-beta3-59255';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-trackback.php b/wp-trackback.php
index 670d9c457b..6a93d059fc 100644
--- a/wp-trackback.php
+++ b/wp-trackback.php
@@ -60,7 +60,14 @@ $blog_name = isset( $_POST['blog_name'] ) ? wp_unslash( $_POST['blog_name'] ) :
 
 if ( $charset ) {
 	$charset = str_replace( array( ',', ' ' ), '', strtoupper( trim( $charset ) ) );
-} else {
+
+	// Validate the specified "sender" charset is available on the receiving site.
+	if ( function_exists( 'mb_list_encodings' ) && ! in_array( $charset, mb_list_encodings(), true ) ) {
+		$charset = '';
+	}
+}
+
+if ( ! $charset ) {
 	$charset = 'ASCII, UTF-8, ISO-8859-1, JIS, EUC-JP, SJIS';
 }