diff --git a/gnu/packages/hurd.scm b/gnu/packages/hurd.scm
index 0e47a954d7..3785c47750 100644
--- a/gnu/packages/hurd.scm
+++ b/gnu/packages/hurd.scm
@@ -746,7 +746,8 @@ in userland processes thanks to the DDE layer.")
                                      ((? target-x86-32?)
                                       "i386")
                                      ((? target-x86-64?)
-                                      "amd64")))
+                                      "amd64")
+                                     (_ "unknown")))
                        (toprump (string-append
                                  (getcwd)
                                  "/buildrump.sh/src/sys/rump"))