diff --git a/classes/class-wc-checkout.php b/classes/class-wc-checkout.php
index 88441c95b05..ea1de29305f 100644
--- a/classes/class-wc-checkout.php
+++ b/classes/class-wc-checkout.php
@@ -145,7 +145,7 @@ class WC_Checkout {
 					switch ($key) :
 						case "billing_postcode" :
 						case "shipping_postcode" :
-							$this->posted[$key] = strtolower(str_replace(' ', '', $this->posted[$key]));
+							$this->posted[$key] = strtoupper(str_replace(' ', '', $this->posted[$key]));
 							
 							if (!$validation->is_postcode( $this->posted[$key], $_POST['billing_country'] )) : $woocommerce->add_error( '<strong>' . $field['label'] . '</strong> ' . __('(billing) is not a valid postcode/ZIP.', 'woocommerce') ); 
 							else :