diff --git a/src/js/assayJS.js b/src/js/assayJS.js
index 9742abb9250f63a8ddbba1a54c695e637cc50c2a..87783dbc9c3e3a29484c4070061052980d88c805 100644
--- a/src/js/assayJS.js
+++ b/src/js/assayJS.js
@@ -115,6 +115,9 @@ globalThis.applyGeneticColor = function(slave) {
  * @param {App.Entity.SlaveState} slave
  */
 globalThis.newSlave = function(slave) {
+	if (getSlave(slave.ID)) {
+		throw "Slave already exists";
+	}
 	if (slave.override_Race !== 1) {
 		slave.origRace = slave.race;
 	}