diff --git a/migrations/20190830204531-tasks-rename-errorMessage-errorJson.js b/migrations/20190830204531-tasks-rename-errorMessage-errorJson.js
index e2ebf5285..be51578e3 100644
--- a/migrations/20190830204531-tasks-rename-errorMessage-errorJson.js
+++ b/migrations/20190830204531-tasks-rename-errorMessage-errorJson.js
@@ -1,9 +1,20 @@
 'use strict';
 
+let async = require('async');
+
 exports.up = function(db, callback) {
     db.runSql('ALTER TABLE tasks CHANGE errorMessage errorJson TEXT', [], function (error) {
         if (error) console.error(error);
-        callback(error);
+
+        // convert error messages into json
+        db.all('SELECT id, errorJson FROM apps', function (error, apps) {
+            async.eachSeries(apps, function (app, iteratorDone) {
+                if (app.errorJson === 'null') return iteratorDone();
+                if (app.errorJson === null) return iteratorDone();
+
+                db.runSql('UPDATE apps SET errorJson = ? WHERE id = ?', [ JSON.stringify({ message: app.errorJson }, app.id)], iteratorDone);
+            }, callback);
+        });
     });
 };
 
diff --git a/src/appdb.js b/src/appdb.js
index a58f924f4..1258ef723 100644
--- a/src/appdb.js
+++ b/src/appdb.js
@@ -104,11 +104,7 @@ function postProcess(result) {
         if (envNames[i]) result.env[envNames[i]] = envValues[i];
     }
 
-    if (result.errorJson === null) {
-        result.error = null;
-    } else {
-        result.error = safe.JSON.parse(result.errorJson) || { message: result.errorJson }; // make legacy error messages are JSON
-    }
+    result.error = safe.JSON.parse(result.errorJson);
     delete result.errorJson;
 
     result.taskId = result.taskId ? String(result.taskId) : null;