diff --git a/member-file.scm b/member-file.scm
index 3592102..009a50d 100644
--- a/member-file.scm
+++ b/member-file.scm
@@ -41,6 +41,7 @@
 	 (chicken io)
 	 (chicken irregex)
 	 (chicken format)
+	 (chicken random)
 	 dictionary
 	 month
 	 period
@@ -66,6 +67,14 @@
 
  (define *member-default-joined* (make-parameter (make-month 2015 1)))
 
+ ;; Symbol used for error reporting in member file keys.
+ (define member-file-error-symbol
+   (string->symbol
+    (sprintf "error-symbol-~A"
+	     (substring
+	      (number->string (pseudo-random-real))
+	      2))))
+
  ;; Derived keys
  (define start/stop-keys-keys
    (map