diff --git a/Documentation/config-accounts.txt b/Documentation/config-accounts.txt
index 6378632..51d8cec 100644
--- a/Documentation/config-accounts.txt
+++ b/Documentation/config-accounts.txt
@@ -296,6 +296,11 @@
 an external ID is used only once (e.g. an external ID can never be
 assigned to multiple accounts at a point in time).
 
+[IMPORTANT]
+If the external ID key is changed manually you must adapt the note key
+to the new SHA1. Otherwise the external ID becomes inconsistent and is
+ignored by Gerrit.
+
 The note content is a Git config file:
 
 ----