diff --git a/ext/numo/narray/gen/tmpl/qsort.c b/ext/numo/narray/gen/tmpl/qsort.c
index 7d51ec41..dffda343 100644
--- a/ext/numo/narray/gen/tmpl/qsort.c
+++ b/ext/numo/narray/gen/tmpl/qsort.c
@@ -128,6 +128,7 @@ static void
         presorted;
 
  loop:SWAPINIT(a, es);
+    if (es >= sizeof(void*)) swaptype = 2;
     if (n < 7)
         {
             for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
diff --git a/test/narray_test.rb b/test/narray_test.rb
index 3a1e2a21..08065ea0 100644
--- a/test/narray_test.rb
+++ b/test/narray_test.rb
@@ -649,4 +649,10 @@ class NArrayTest < Test::Unit::TestCase
     assert_equal(Numo::DFloat[1, Float::NAN, 3].format_to_a,
                  Numo::DFloat.cast(Numo::RObject[1, nil, 3]).format_to_a)
   end
+
+  test "sort_index correctness" do
+    a = Numo::SFloat.new(10).rand_norm
+    idx = a.sort_index
+    assert { a[idx].to_a == a[idx].to_a.sort }
+  end
 end