diff --git a/wp-includes/meta.php b/wp-includes/meta.php
index e1c1f92e48..fe144fcda6 100644
--- a/wp-includes/meta.php
+++ b/wp-includes/meta.php
@@ -1159,7 +1159,8 @@ function _get_meta_table( $type ) {
  * @return bool Whether the meta key is considered protected.
  */
 function is_protected_meta( $meta_key, $meta_type = '' ) {
-	$protected = ( '_' === $meta_key[0] );
+	$sanitized_key = preg_replace( "/[^\x20-\x7E\p{L}]/", '', $meta_key );
+	$protected     = strlen( $sanitized_key ) > 0 && ( '_' === $sanitized_key[0] );
 
 	/**
 	 * Filters whether a meta key is considered protected.
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 905e6d8c04..9b826bf034 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-beta2-49386';
+$wp_version = '5.6-beta2-49387';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.