diff --git a/plugins/woocommerce/changelog/fix-shipping-postcode-50800 b/plugins/woocommerce/changelog/fix-shipping-postcode-50800
new file mode 100644
index 00000000000..84f5873325b
--- /dev/null
+++ b/plugins/woocommerce/changelog/fix-shipping-postcode-50800
@@ -0,0 +1,4 @@
+Significance: patch
+Type: fix
+
+Fix postcode validation within the legacy cart show_shipping method.
diff --git a/plugins/woocommerce/includes/class-wc-cart.php b/plugins/woocommerce/includes/class-wc-cart.php
index db8fefc926b..8c75b5fc4eb 100644
--- a/plugins/woocommerce/includes/class-wc-cart.php
+++ b/plugins/woocommerce/includes/class-wc-cart.php
@@ -1597,7 +1597,7 @@ class WC_Cart extends WC_Legacy_Cart {
 			 */
 			$postcode_enabled  = apply_filters( 'woocommerce_shipping_calculator_enable_postcode', true );
 			$postcode_required = isset( $country_fields['shipping_postcode'] ) && $country_fields['shipping_postcode']['required'];
-			if ( $postcode_enabled && $postcode_required && ! $this->get_customer()->get_shipping_postcode() ) {
+			if ( $postcode_enabled && $postcode_required && '' === $this->get_customer()->get_shipping_postcode() ) {
 				return false;
 			}
 		}