diff --git a/gnu/system/linux-container.scm b/gnu/system/linux-container.scm
index c558f45769..3acc579a6b 100644
--- a/gnu/system/linux-container.scm
+++ b/gnu/system/linux-container.scm
@@ -57,7 +57,8 @@ (define user-file-systems
                     (source (file-system-device fs)))
                 (or (string=? target (%store-prefix))
                     (string=? target "/")
-                    (string-prefix? "/dev/" source)
+                    (and (string? source)
+                         (string-prefix? "/dev/" source))
                     (string-prefix? "/dev" target)
                     (string-prefix? "/sys" target))))
             (operating-system-file-systems os)))