diff --git a/basis/compiler/cfg/def-use/def-use.factor b/basis/compiler/cfg/def-use/def-use.factor
index 3838a0d1b9..87758fafcd 100644
--- a/basis/compiler/cfg/def-use/def-use.factor
+++ b/basis/compiler/cfg/def-use/def-use.factor
@@ -6,6 +6,7 @@ namespaces quotations sequences sets slots words
 compiler.cfg.instructions compiler.cfg.instructions.syntax
 compiler.cfg.rpo ;
 FROM: namespaces => set ;
+FROM: sets => members ;
 IN: compiler.cfg.def-use
 
 GENERIC: defs-vreg ( insn -- vreg/f )
@@ -95,9 +96,9 @@ SYMBOLS: defs insns uses ;
     cfg [| block |
         block instructions>> [
             dup ##phi?
-            [ inputs>> [ use conjoin-at ] assoc-each ]
-            [ uses-vregs [ block swap use conjoin-at ] each ]
+            [ inputs>> [ use adjoin-at ] assoc-each ]
+            [ uses-vregs [ block swap use adjoin-at ] each ]
             if
         ] each
     ] each-basic-block
-    use [ keys ] assoc-map uses set ;
+    use [ members ] assoc-map uses set ;