diff --git a/module/srfi/srfi-13.mes b/module/srfi/srfi-13.mes
index 974844a3..0bd8c543 100644
--- a/module/srfi/srfi-13.mes
+++ b/module/srfi/srfi-13.mes
@@ -87,3 +87,6 @@
               (loop (cdr lst) (1- i)))))))
 
 (define reverse-list->string (compose list->string reverse))
+
+(define substring/copy substring)
+(define substring/shared substring)