diff --git a/oop.h b/oop.h
index 6accaacb1f738dd4b3837cddeb5b09e88138ff58..5ac50939608e93d691f6894c60f8804f07ccf391 100644
--- a/oop.h
+++ b/oop.h
@@ -56,6 +56,7 @@ struct oop_source {
 /* For recommended use by oop components. */
 
 extern void *(*oop_malloc)(size_t);
+extern void *(*oop_realloc)(void *,size_t);
 extern void (*oop_free)(void *);
 
 /* ------------------------------------------------------------------------- */