diff --git a/src/pair.c b/src/pair.c
index 80ac57a4..e461ba70 100644
--- a/src/pair.c
+++ b/src/pair.c
@@ -138,17 +138,17 @@ pic_value
 pic_append(pic_state *pic, pic_value xs, pic_value ys)
 {
   int ai = pic_gc_arena_preserve(pic);
+  pic_value x;
 
-  if (pic_nil_p(xs)) {
-    return ys;
-  }
-  else {
-    xs = pic_cons(pic, pic_car(pic, xs), pic_append(pic, pic_cdr(pic, xs), ys));
-  }
+  xs = pic_reverse(pic, xs);
+  pic_for_each (x, xs) {
+    ys = pic_cons(pic, x, ys);
 
-  pic_gc_arena_restore(pic, ai);
-  pic_gc_protect(pic, xs);
-  return xs;
+    pic_gc_arena_restore(pic, ai);
+    pic_gc_protect(pic, xs);
+    pic_gc_protect(pic, ys);
+  }
+  return ys;
 }
 
 pic_value