diff --git a/schemas/taskrunfinished.json b/schemas/taskrunfinished.json
index 580e707..a18a91e 100644
--- a/schemas/taskrunfinished.json
+++ b/schemas/taskrunfinished.json
@@ -90,7 +90,8 @@
               ]
             },
             "outcome": {
-              "type": "string"
+              "type": "string",
+              "enum": ["success", "failure", "cancel", "error"]
             },
             "errors": {
               "type": "string"