diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index 81a9c8dfa..460a91264 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -83,6 +83,12 @@ the application must enable it using the
 operation.
 This operation allows a handshake between the kernel and user space
 to determine the API version and supported features.
+This operation must be performed before any of the other
+.BR ioctl (2)
+operations described below (or those operations fail with the
+.BR EINVAL
+error).
+
 After a successful
 .B UFFDIO_API
 operation,