diff --git a/core/compiler/units/units.factor b/core/compiler/units/units.factor
index 11c81f4097..729cfcd179 100755
--- a/core/compiler/units/units.factor
+++ b/core/compiler/units/units.factor
@@ -1,7 +1,7 @@
 ! Copyright (C) 2008 Slava Pestov.
 ! See http://factorcode.org/license.txt for BSD license.
 USING: kernel continuations assocs namespaces sequences words
-vocabs definitions hashtables init ;
+vocabs definitions hashtables init sets ;
 IN: compiler.units
 
 SYMBOL: old-definitions