diff --git a/classes/abstracts/abstract-wc-product.php b/classes/abstracts/abstract-wc-product.php
index 9bf7438853f..b84f4627eac 100644
--- a/classes/abstracts/abstract-wc-product.php
+++ b/classes/abstracts/abstract-wc-product.php
@@ -637,7 +637,7 @@ class WC_Product {
 	 * @return bool
 	 */
 	function is_on_sale() {
-		return $this->sale_price && $this->sale_price == $this->price ? true : false;
+		return isset( $this->sale_price ) && $this->sale_price == $this->price ? true : false;
 	}