diff --git a/includes/wc-formatting-functions.php b/includes/wc-formatting-functions.php
index 967bb207f343c..cc5d0f6872d6e 100644
--- a/includes/wc-formatting-functions.php
+++ b/includes/wc-formatting-functions.php
@@ -713,6 +713,11 @@ function wc_string_to_datetime( $time_string ) {
  * @return string PHP timezone string for the site
  */
 function wc_timezone_string() {
+	// Added in WordPress 5.3 Ref https://developer.wordpress.org/reference/functions/wp_timezone_string/.
+	if ( function_exists( 'wp_timezone_string' ) ) {
+		return wp_timezone_string();
+	}
+
 	// If site timezone string exists, return it.
 	$timezone = get_option( 'timezone_string' );
 	if ( $timezone ) {
@@ -720,13 +725,13 @@ function wc_timezone_string() {
 	}
 
 	// Get UTC offset, if it isn't set then return UTC.
-	$utc_offset = intval( get_option( 'gmt_offset', 0 ) );
-	if ( 0 === $utc_offset ) {
+	$utc_offset = floatval( get_option( 'gmt_offset', 0 ) );
+	if ( ! is_numeric( $utc_offset ) || 0.0 === $utc_offset ) {
 		return 'UTC';
 	}
 
 	// Adjust UTC offset from hours to seconds.
-	$utc_offset *= 3600;
+	$utc_offset = (int) ( $utc_offset * 3600 );
 
 	// Attempt to guess the timezone string from the UTC offset.
 	$timezone = timezone_name_from_abbr( '', $utc_offset );
diff --git a/tests/legacy/unit-tests/formatting/functions.php b/tests/legacy/unit-tests/formatting/functions.php
index a2e517dfea45a..a88a086ee02f9 100644
--- a/tests/legacy/unit-tests/formatting/functions.php
+++ b/tests/legacy/unit-tests/formatting/functions.php
@@ -699,15 +699,15 @@ public function test_wc_timezone_string() {
 
 		// Test with missing UTC offset.
 		delete_option( 'gmt_offset' );
-		$this->assertEquals( 'UTC', wc_timezone_string() );
+		$this->assertEquals( '+00:00', wc_timezone_string() );
 
 		// Test with manually set UTC offset.
 		update_option( 'gmt_offset', -4 );
 		$this->assertNotEquals( 'UTC', wc_timezone_string() );
 
 		// Test with invalid offset.
-		update_option( 'gmt_offset', 99 );
-		$this->assertEquals( 'UTC', wc_timezone_string() );
+		update_option( 'gmt_offset', 'invalid' );
+		$this->assertEquals( '+00:00', wc_timezone_string() );
 
 		// Restore default.
 		update_option( 'gmt_offset', '0' );