diff --git a/basis/tr/tr.factor b/basis/tr/tr.factor
index a76bf80dc2..8a95ea5e53 100644
--- a/basis/tr/tr.factor
+++ b/basis/tr/tr.factor
@@ -18,7 +18,7 @@ M: bad-tr summary
     [ [ ascii? ] all? ] both? [ bad-tr ] unless ;
 
 : compute-tr ( quot from to -- mapping )
-    [ 128 iota ] 3dip zip
+    [ 128 iota ] 3dip { } zip-as
     '[ [ _ call( x -- y ) _ at ] keep or ] B{ } map-as ; inline
 
 : tr-hints ( word -- )