diff --git a/packages/input_schema/src/schema.json b/packages/input_schema/src/schema.json
index b76db6311..b9f978bc1 100644
--- a/packages/input_schema/src/schema.json
+++ b/packages/input_schema/src/schema.json
@@ -66,7 +66,8 @@
 
                 "enum": {
                     "type": "array",
-                    "items": { "type": "string" }
+                    "items": { "type": "string" },
+                    "uniqueItems": true
                 },
                 "enumTitles": {
                     "type": "array",