diff --git a/src/pretix/api/exception.py b/src/pretix/api/exception.py
index 47869e7f4..5c1f033ba 100644
--- a/src/pretix/api/exception.py
+++ b/src/pretix/api/exception.py
@@ -10,7 +10,10 @@ def custom_exception_handler(exc, context):
     if isinstance(exc, LockTimeoutException):
         response = Response(
             {'detail': 'The server was too busy to process your request. Please try again.'},
-            status=status.HTTP_409_CONFLICT
+            status=status.HTTP_409_CONFLICT,
+            headers={
+                'Retry-After': 5
+            }
         )
 
     return response