diff --git a/gnu/system/pam.scm b/gnu/system/pam.scm
index 75edd01908..128b2bb0fe 100644
--- a/gnu/system/pam.scm
+++ b/gnu/system/pam.scm
@@ -208,14 +208,16 @@ dumped in /etc/pam.d/NAME, where NAME is the name of SERVICE."
         (env  (pam-entry ; to honor /etc/environment.
                (control "required")
                (module "pam_env.so"))))
-    (lambda* (name #:key allow-empty-passwords? (allow-root? #f) motd
-                   login-uid? (gnupg? #f))
+    (lambda* (name #:key allow-empty-passwords? allow-root? motd
+              login-uid? gnupg?)
       "Return a standard Unix-style PAM service for NAME.  When
 ALLOW-EMPTY-PASSWORDS? is true, allow empty passwords.  When ALLOW-ROOT? is
 true, allow root to run the command without authentication.  When MOTD is
 true, it should be a file-like object used as the message-of-the-day.
 When LOGIN-UID? is true, require the 'pam_loginuid' module; that module sets
-/proc/self/loginuid, which the libc 'getlogin' function relies on."
+/proc/self/loginuid, which the libc 'getlogin' function relies on.  When
+GNUPG? is true, require the 'pam_gnupg.so' module; that module hands over
+login password to 'gpg-agent'."
       ;; See <http://www.linux-pam.org/Linux-PAM-html/sag-configuration-example.html>.
       (pam-service
        (name name)