diff --git a/io.c b/io.c
index 3ac6b97a0e..bd21e9460e 100644
--- a/io.c
+++ b/io.c
@@ -4945,7 +4945,7 @@ internal_pwrite_func(void *ptr)
  *     File.read("out")        #=> "\u0000\u0000\u0000ABCDEF"
  */
 static VALUE
-rb_io_pwrite(VALUE io, VALUE offset, VALUE str)
+rb_io_pwrite(VALUE io, VALUE str, VALUE offset)
 {
     rb_io_t *fptr;
     ssize_t n;
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index d6cbf205e9..ac7570a2b3 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -3541,7 +3541,7 @@ __END__
     def test_pwrite
       make_tempfile { |t|
         open(t.path, IO::RDWR) do |f|
-          assert_equal(3, f.pwrite(4, "ooo"))
+          assert_equal(3, f.pwrite("ooo", 4))
           assert_equal("ooo", f.pread(3, 4))
         end
       }