diff --git a/src/pretix/base/models/invoices.py b/src/pretix/base/models/invoices.py
index 7e3a38d46..5733abc25 100644
--- a/src/pretix/base/models/invoices.py
+++ b/src/pretix/base/models/invoices.py
@@ -233,3 +233,6 @@ class InvoiceLine(models.Model):
 
     class Meta:
         ordering = ('position', 'pk')
+
+    def __str__(self):
+        return 'Line {} of invoice {}'.format(self.position, self.invoice)
diff --git a/src/pretix/base/models/orders.py b/src/pretix/base/models/orders.py
index 59d9235a7..283f84e45 100644
--- a/src/pretix/base/models/orders.py
+++ b/src/pretix/base/models/orders.py
@@ -1037,6 +1037,9 @@ class OrderPayment(models.Model):
     class Meta:
         ordering = ('local_id',)
 
+    def __str__(self):
+        return self.full_id
+
     @property
     def info_data(self):
         """
@@ -1343,6 +1346,9 @@ class OrderRefund(models.Model):
     class Meta:
         ordering = ('local_id',)
 
+    def __str__(self):
+        return self.full_id
+
     @property
     def info_data(self):
         """