diff --git a/member-parser.scm b/member-parser.scm
index 6f57e8f..07899a3 100644
--- a/member-parser.scm
+++ b/member-parser.scm
@@ -86,7 +86,12 @@
 		  mr1
 		  (member-record-add-highlight mr1 line-number msg 3 'error))))
 	   ((joined)
-	    (member-record-sub-set mr output key (string->month (car value))))
+	    (let* ((month (string->month (car value)))
+		   (mr0 (member-record-sub-set mr output key month)))
+	      (if month
+		  mr0
+		  (member-record-add-highlight
+		   mr0 (cdr value) "Invalid month specification" 3 'error))))
 	   ((card desfire)
 	    (member-record-sub-set mr output key
 				   (map