diff --git a/wp-includes/fonts/class-wp-font-utils.php b/wp-includes/fonts/class-wp-font-utils.php
index 3c2d5057e4..6e91440748 100644
--- a/wp-includes/fonts/class-wp-font-utils.php
+++ b/wp-includes/fonts/class-wp-font-utils.php
@@ -110,8 +110,11 @@ class WP_Font_Utils {
 			'unicodeRange' => 'U+0-10FFFF',
 		);
 		$settings = wp_parse_args( $settings, $defaults );
-
-		$font_family   = mb_strtolower( $settings['fontFamily'] );
+		if ( function_exists( 'mb_strtolower' ) ) {
+			$font_family = mb_strtolower( $settings['fontFamily'] );
+		} else {
+			$font_family = strtolower( $settings['fontFamily'] );
+		}
 		$font_style    = strtolower( $settings['fontStyle'] );
 		$font_weight   = strtolower( $settings['fontWeight'] );
 		$font_stretch  = strtolower( $settings['fontStretch'] );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 51bb22d56d..814a3fa3e4 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6-alpha-57864';
+$wp_version = '6.6-alpha-57865';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.