diff --git a/README b/README
index a5ce54bec7..c0d8fce550 100644
--- a/README
+++ b/README
@@ -73,6 +73,9 @@ REQUIREMENTS:
         Note that systemd-localed.service and other systemd units use
         PrivateNetwork and PrivateDevices so this is effectively required.
 
+        Required for PrivateUsers in service units:
+          CONFIG_USER_NS
+
         Optional but strongly recommended:
           CONFIG_IPV6
           CONFIG_AUTOFS4_FS