diff --git a/nbde/system/installed-base.scm b/nbde/system/installed-base.scm
index 783428d..1061c54 100644
--- a/nbde/system/installed-base.scm
+++ b/nbde/system/installed-base.scm
@@ -19,7 +19,7 @@
 (define* (nbde-installed-operating-system #:key
                                           host-name
                                           bootloader
-                                          mapped-devices
+                                          (mapped-devices '())
                                           file-systems
                                           initrd
                                           interface