diff --git a/tests/test-class-wp-web-app-manifest.php b/tests/test-class-wp-web-app-manifest.php
index 6575f5bf4..473e0fd16 100644
--- a/tests/test-class-wp-web-app-manifest.php
+++ b/tests/test-class-wp-web-app-manifest.php
@@ -581,6 +581,8 @@ public function get_data_to_test_sanitize_short_name() {
 			'whitespace_padding' => array( '     WP Dev ', 'WP Dev' ),
 			'script_contains'    => array( 'WP <script>evil</script> Dev ', 'WP Dev' ),
 			'too_long'           => array( 'WordPress Develop', 'WordPress De' ),
+			'multi-byte'         => array( 'On the Rhône', 'On the Rhône' ),
+			'emoji'              => array( '👌👌👌👌👌👌👌👌👌👌👌👌👌👌', '👌👌👌👌👌👌👌👌👌👌👌👌' ), // 👌 takes 4 bytes.
 		);
 	}
 
diff --git a/wp-includes/class-wp-web-app-manifest.php b/wp-includes/class-wp-web-app-manifest.php
index c3045e737..3acb5c078 100644
--- a/wp-includes/class-wp-web-app-manifest.php
+++ b/wp-includes/class-wp-web-app-manifest.php
@@ -575,7 +575,7 @@ public function sanitize_short_name( $value ) {
 			return '';
 		}
 		$value = trim( sanitize_text_field( $value ) );
-		return (string) substr( $value, 0, self::SHORT_NAME_MAX_LENGTH );
+		return (string) mb_substr( $value, 0, self::SHORT_NAME_MAX_LENGTH );
 	}
 
 	/**