diff --git a/doc/manuals/osmopcu-gb.adoc b/doc/manuals/osmopcu-gb.adoc
index fc2ca8f..64316a2 100644
--- a/doc/manuals/osmopcu-gb.adoc
+++ b/doc/manuals/osmopcu-gb.adoc
@@ -1,3 +1,5 @@
+:gfdl-enabled:
+
 OsmoPCU Gb Protocol Specification
 =================================
 Harald Welte <hwelte@sysmocom.de>