diff --git a/basis/classes/struct/prettyprint/prettyprint.factor b/basis/classes/struct/prettyprint/prettyprint.factor
index 0de56f4ce6..58c923e6d0 100644
--- a/basis/classes/struct/prettyprint/prettyprint.factor
+++ b/basis/classes/struct/prettyprint/prettyprint.factor
@@ -116,3 +116,5 @@ M: struct-mirror >alist ( mirror -- alist )
     ] bi append ;
 
 M: struct make-mirror <struct-mirror> ;
+
+INSTANCE: struct-mirror assoc