diff --git a/src/appdb.js b/src/appdb.js
index 1e3d32dbe..52071a000 100644
--- a/src/appdb.js
+++ b/src/appdb.js
@@ -104,7 +104,7 @@ function postProcess(result) {
         if (envNames[i]) result.env[envNames[i]] = envValues[i];
     }
 
-    result.error = safe.JSON.parse(result.errorJson);
+    result.error = safe.JSON.parse(result.errorJson) || { message: result.errorJson }; // make legacy error messages are JSON
     delete result.errorJson;
 
     result.taskId = result.taskId ? String(result.taskId) : null;