diff --git a/src/pretix/base/views/tasks.py b/src/pretix/base/views/tasks.py
index 7220c4d81a..0c0514ce84 100644
--- a/src/pretix/base/views/tasks.py
+++ b/src/pretix/base/views/tasks.py
@@ -106,7 +106,7 @@ class AsyncMixin:
         elif res.state == 'PROGRESS':
             data.update({
                 'started': True,
-                'percentage': res.result.get('value', 0) if res.result else 0
+                'percentage': res.result.get('value', 0) if isinstance(res.result, dict) else 0
             })
         elif res.state == 'STARTED':
             data.update({