diff --git a/pl/sort.yap b/pl/sort.yap
index d4e9607f3..91eee683e 100644
--- a/pl/sort.yap
+++ b/pl/sort.yap
@@ -37,9 +37,9 @@ length(L,M) :- '$$_length2'(M,L).
 		->
           L = []
         ;
-	  L = [_|L1],
 	  N > 0,
 	  N1 is N - 1,
+	  L = [_|L1],
 	  '$$_length2'(N1, L1)
         ).