diff --git a/core/math/math.factor b/core/math/math.factor
index b23e129946..62aadea546 100644
--- a/core/math/math.factor
+++ b/core/math/math.factor
@@ -147,7 +147,7 @@ ERROR: log2-expects-positive x ;
 : even? ( n -- ? ) 1 bitand zero? ; inline
 : odd? ( n -- ? ) 1 bitand 1 number= ; inline
 
-GENERIC: neg? ( x -- -x )
+GENERIC: neg? ( x -- ? )
 
 : if-zero ( ..a n quot1: ( ..a -- ..b ) quot2: ( ..a n -- ..b ) -- ..b )
     [ dup zero? ] [ [ drop ] prepose ] [ ] tri* if ; inline