diff --git a/extra/assocs/extras/extras.factor b/extra/assocs/extras/extras.factor
index 54e28e8c02..3019a5e86a 100644
--- a/extra/assocs/extras/extras.factor
+++ b/extra/assocs/extras/extras.factor
@@ -21,3 +21,6 @@ IN: assocs.extras
         [ dup length ] dip new-assoc
         [ [ set-at ] with-assoc 2each ] keep
     ] if ; inline
+
+: substitute! ( seq assoc -- seq )
+    substituter map! ;