diff --git a/src/js/surgery.js b/src/js/surgery.js
index 66ab1e64a132a3a7467186e3f42361e8e07ed672..053f9d45f17a45ded60dc9504261f5cd64504e50 100644
--- a/src/js/surgery.js
+++ b/src/js/surgery.js
@@ -702,9 +702,9 @@ window.setGeneticEyeColor = function(slave, color, heterochromia = false) {
  * Takes heterochromia and albinism into account.
  *
  * @param {App.Entity.SlaveState} slave
- * @param {string} side
+ * @param {string} [side]
  */
-window.resetEyeColor = function(slave, side) {
+window.resetEyeColor = function(slave, side = "both") {
 	if (side === "both") {
 		resetEyeColor(slave, "left");
 		resetEyeColor(slave, "right");