diff --git a/core/sequences/sequences.factor b/core/sequences/sequences.factor
index 31c7c8a4d7..40a8892e8b 100644
--- a/core/sequences/sequences.factor
+++ b/core/sequences/sequences.factor
@@ -828,7 +828,7 @@ PRIVATE>
 
 : supremum ( seq -- n ) dup first [ max ] reduce ;
 
-: sigma ( seq quot -- n ) [ + ] compose 0 swap reduce ; inline
+: sigma ( seq quot -- n ) 0 -rot [ rot slip + ] curry each ; inline
 
 : count ( seq quot -- n ) [ 1 0 ? ] compose sigma ; inline