diff --git a/basis/math/combinatorics/combinatorics.factor b/basis/math/combinatorics/combinatorics.factor
index e091b18329..baa401cd71 100644
--- a/basis/math/combinatorics/combinatorics.factor
+++ b/basis/math/combinatorics/combinatorics.factor
@@ -253,9 +253,9 @@ PRIVATE>
 
 :: next-selection ( seq n -- )
     1 seq length 1 - [
-        over 0 =
+        dup 0 >= [ over 0 = ] [ t ] if
     ] [
-        [ seq [ + n /mod ] change-nth-unsafe ] keep 1 -
+        [ seq [ + n /mod ] change-nth ] keep 1 -
     ] do until 2drop ; inline
 
 :: (selections) ( seq n -- selections )