diff --git a/gnu/machine/ssh.scm b/gnu/machine/ssh.scm
index 23ae917b79..1b88fb44cc 100644
--- a/gnu/machine/ssh.scm
+++ b/gnu/machine/ssh.scm
@@ -103,6 +103,9 @@ (define (machine-ssh-session machine)
               (port (machine-ssh-configuration-port config))
               (identity (machine-ssh-configuration-identity config))
               (host-key (machine-ssh-configuration-host-key config)))
+          (unless host-key
+            (warning (G_ "<machine-ssh-configuration> without a 'host-key' \
+is deprecated~%")))
           (open-ssh-session host-name
                             #:user user
                             #:port port