diff --git a/modules/ces/system-manager.scm b/modules/ces/system-manager.scm
index 54419e2..9e21b6d 100644
--- a/modules/ces/system-manager.scm
+++ b/modules/ces/system-manager.scm
@@ -38,26 +38,27 @@
 (define (add-system-to-system-manager sys-manager sys)
   "Returns a new system manager with sys added,
 or false if the input is invalid."
-  (let ((proc-table (system-manager-proc-table sys-manager))
-        (old-systems (systems sys-manager)))
-    (if (and (system-manager? sys-manager)
-             (system? sys))
-        (make-system-manager (cons sys old-systems)
-                             proc-table)
-        (error "Invalid inputs to add-system-to-system-manager"
-               sys-manager sys))))
+  (if (and (system-manager? sys-manager)
+           (system? sys))
+      (let ((proc-table (system-manager-proc-table sys-manager))
+            (old-systems (systems sys-manager)))
+        (make-system-manager (cons sys old-systems) proc-table))
+      (error "Invalid inputs to add-system-to-system-manager" sys-manager sys)))
 
 (define create-system-manager
   (case-lambda
     (()
      (make-system-manager '() (make-eq-hashtable)))
     ((sys-list)
-     (fold (lambda (manager sys)
-             (if (system? sys)
-                 (add-system-to-system-manager manager sys)
-                 manager))
-           (create-system-manager)
-           sys-list))))
+     (cond
+      ((list? sys-list)
+       (fold (lambda (manager sys)
+               (when (system? sys)
+                 (add-system-to-system-manager manager sys)))
+             (create-system-manager)
+             sys-list))
+      (else (error "Incorrect parameter passed to create-system-manager"
+                   sys-list))))))
 
 (define (get-procs-from-table sys-manager entity)
   (if (and (system-manager? sys-manager)