diff --git a/src/wp-includes/formatting.php b/src/wp-includes/formatting.php
index 0441866344..eb4acda64b 100644
--- a/src/wp-includes/formatting.php
+++ b/src/wp-includes/formatting.php
@@ -4639,11 +4639,11 @@ EOF;
 	$safe_text = (string) preg_replace_callback(
 		$regex,
 		static function( $matches ) {
-			if ( ! $matches[0] ) {
+			if ( ! isset( $matches[0] ) ) {
 				return '';
 			}
 
-			if ( ! empty( $matches['non_cdata'] ) ) {
+			if ( isset( $matches['non_cdata'] ) ) {
 				// escape HTML entities in the non-CDATA Section.
 				return _wp_specialchars( $matches['non_cdata'], ENT_XML1 );
 			}
diff --git a/tests/phpunit/tests/formatting/escXml.php b/tests/phpunit/tests/formatting/escXml.php
index fa6738dca0..435bc398a6 100644
--- a/tests/phpunit/tests/formatting/escXml.php
+++ b/tests/phpunit/tests/formatting/escXml.php
@@ -42,6 +42,11 @@ class Tests_Formatting_EscXml extends WP_UnitTestCase {
 				"SELECT meta_key, meta_value FROM wp_trunk_sitemeta WHERE meta_key IN ('site_name', 'siteurl', 'active_sitewide_plugins', '_site_transient_timeout_theme_roots', '_site_transient_theme_roots', 'site_admins', 'can_compress_scripts', 'global_terms_enabled') AND site_id = 1",
 				'SELECT meta_key, meta_value FROM wp_trunk_sitemeta WHERE meta_key IN ('site_name', 'siteurl', 'active_sitewide_plugins', '_site_transient_timeout_theme_roots', '_site_transient_theme_roots', 'site_admins', 'can_compress_scripts', 'global_terms_enabled') AND site_id = 1',
 			),
+			// Zero string.
+			array(
+				'0',
+				'0',
+			),
 		);
 	}