diff --git a/1to2.md b/1to2.md
index 7a708f45..b95deaef 100644
--- a/1to2.md
+++ b/1to2.md
@@ -46,6 +46,10 @@ Start Radicale 1.x.x as you would normally do, but add the argument
 into the specified folder. This folder can be directly used with the
 default storage backend of Radicale 2.x.x.
 
+If you import big calendars or address books into Radicale 2.x.x the first
+request might take a long time, because it has to initialize its internal
+caches. Clients can time out, subsequent requests will be much faster.
+
 You can install version 1.1.6 with:
 
 ```shell