diff --git a/README.md b/README.md
index b926f23..5bb82cc 100644
--- a/README.md
+++ b/README.md
@@ -306,10 +306,10 @@ A packed list is a list of varints.
 Complete file structure
 -----------------------
 
-`idx_*` sections are of type `[]u29` and are pointing to the respective
-`Groups` and `Users` entries (from the beginning of the respective section).
-Since User and Group records are 8-byte aligned, 3 bits are saved from every
-element.
+`idx_*` sections are of type `[]PackedIntArray(u29)` and are pointing to the
+respective `Groups` and `Users` entries (from the beginning of the respective
+section). Since User and Group records are 8-byte aligned, 3 bits are saved
+from every element.
 
 Each section is padded to 64 bytes.