diff --git a/README.md b/README.md
index ac31f58..455f644 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,8 @@
 its current IMSI with the new one, and uses it in the next location update.
 Afterwards, the HLR will generate the next IMSI and so on.
 
+**FIXME:** details below need updating, see [OS#4400](https://osmocom.org/issues/4400).
+
 ```
 HLR <-> SIM  LOCATION UPDATE, imsi_pseudo=200
 HLR  -> SIM  NEW PSEUDO IMSI REQ, session_id=1, imsi_pseudo=123
diff --git a/docs/specification.md b/docs/specification.md
index 7d4c9bc..3f8b53c 100644
--- a/docs/specification.md
+++ b/docs/specification.md
@@ -1,5 +1,7 @@
 # [WIP] Make IMSI Pseudonymization an optional extension of 3GPP TS
 
+**FIXME:** needs to be updated, see [OS#4400](https://osmocom.org/issues/4400).
+
 Optional additions we need to make, and where to make them:
 
 * Initial provisioning of the SIM: can optionally have a pseudo IMSI