diff --git a/wp-includes/option.php b/wp-includes/option.php
index c813695030..4df0b81458 100644
--- a/wp-includes/option.php
+++ b/wp-includes/option.php
@@ -2903,7 +2903,10 @@ function unregister_setting( $option_group, $option_name, $deprecated = '' ) {
 		$option_group = 'reading';
 	}
 
-	$pos = array_search( $option_name, (array) $new_allowed_options[ $option_group ], true );
+	$pos = false;
+	if ( isset( $new_allowed_options[ $option_group ] ) ) {
+		$pos = array_search( $option_name, (array) $new_allowed_options[ $option_group ], true );
+	}
 
 	if ( false !== $pos ) {
 		unset( $new_allowed_options[ $option_group ][ $pos ] );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 0b8b50392f..aa4d904018 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-beta2-56816';
+$wp_version = '6.4-beta2-56817';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.