diff --git a/extra/math/extras/extras.factor b/extra/math/extras/extras.factor
index 4766eb65f0..29bc5dffea 100644
--- a/extra/math/extras/extras.factor
+++ b/extra/math/extras/extras.factor
@@ -292,7 +292,7 @@ M: real round-away-from-zero
 
 <PRIVATE
 
-: kahan+ ( c n elt -- c' n' )
+: kahan+ ( c sum elt -- c' sum' )
     rot - 2dup + [ -rot [ - ] bi@ ] keep ;
 
 PRIVATE>