diff --git a/core/optimizer/inlining/inlining.factor b/core/optimizer/inlining/inlining.factor
index 9e8f805acf..bbeb5e044f 100755
--- a/core/optimizer/inlining/inlining.factor
+++ b/core/optimizer/inlining/inlining.factor
@@ -48,7 +48,7 @@ DEFER: (flat-length)
             { [ dup word? ] [ word-flat-length ] }
             [ drop 1 ]
         } cond
-    ] map sum ;
+    ] sigma ;
 
 : flat-length ( seq -- n )
     [ word-def (flat-length) ] with-scope ;