diff --git a/librarian_server/api/checkin.py b/librarian_server/api/checkin.py
index f2dc074..600daf9 100644
--- a/librarian_server/api/checkin.py
+++ b/librarian_server/api/checkin.py
@@ -77,11 +77,17 @@ def modify_transfers_by_id(
             reasons.add("No destination transfer with the appropriate ID was found.")
             continue
 
-        authorized = (
-            user.is_admin
-            or (transfer.source == user.username)
-            or (transfer.uploader == user.username)
-        )
+        authorized = user.is_admin
+
+        # IncomingTransfers
+        try:
+            authorized = (
+                authorized
+                or (transfer.source == user.username)
+                or (transfer.uploader == user.username)
+            )
+        except AttributeError:
+            pass
 
         # OutgoingTransfers
         try:
@@ -125,11 +131,17 @@ def get_status_by_id(
     for transfer_id in transfer_ids:
         transfer = session.get(transfer_type, transfer_id, with_for_update=True)
 
-        authorized = (
-            user.is_admin
-            or (transfer.source == user.username)
-            or (transfer.uploader == user.username)
-        )
+        authorized = user.is_admin
+
+        # IncomingTransfers
+        try:
+            authorized = (
+                authorized
+                or (transfer.source == user.username)
+                or (transfer.uploader == user.username)
+            )
+        except AttributeError:
+            pass
 
         # OutgoingTransfers
         try: