diff --git a/includes/class-wc-validation.php b/includes/class-wc-validation.php
index c0b6ce63e49..6e809c70e56 100644
--- a/includes/class-wc-validation.php
+++ b/includes/class-wc-validation.php
@@ -94,7 +94,7 @@ class WC_Validation {
 				$valid = (bool) preg_match( '/^([0-9]{3})(\s?)([0-9]{2})$/', $postcode );
 				break;
 			case 'NL':
-				$valid = (bool) preg_match( '/^[1-9][0-9]{3}\s(?!SA|SD|SS)[A-Z]{2}$/', $postcode );
+				$valid = (bool) preg_match( '/^([1-9][0-9]{3})(\s?)(?!SA|SD|SS|sa|sd|ss)[A-Za-z]{2}$/', $postcode );
 				break;
 
 			default: