diff --git a/src/pretix/base/templatetags/oneline.py b/src/pretix/base/templatetags/oneline.py
index 91396e1346..bbfc848a92 100644
--- a/src/pretix/base/templatetags/oneline.py
+++ b/src/pretix/base/templatetags/oneline.py
@@ -24,6 +24,8 @@ from django import template
 register = template.Library()
 
 
-@register.simple_tag
+@register.filter
 def oneline(value):
-    return ', '.join([l.strip() for l in value.splitlines() if l and l.strip()])
+    if not value:
+        return ''
+    return ', '.join([l.strip() for l in str(value).splitlines() if l and l.strip()])