diff --git a/io.c b/io.c
index e007512..7f55fa2 100644
--- a/io.c
+++ b/io.c
@@ -6365,7 +6365,17 @@ rb_io_reopen(int argc, VALUE *argv, VALUE file)
     }

     if (!NIL_P(nmode)) {
-       int fmode = rb_io_modestr_fmode(StringValueCStr(nmode));
+       VALUE intmode;
+       int fmode;
+
+       if (!NIL_P(intmode = rb_check_to_integer(nmode, "to_int"))) {
+           oflags = NUM2INT(intmode);
+           fmode = rb_io_oflags_fmode(oflags);
+       }
+       else {
+           fmode = rb_io_modestr_fmode(StringValueCStr(nmode));
+       }
+
        if (IS_PREP_STDIO(fptr) &&
             ((fptr->mode & FMODE_READWRITE) & (fmode & FMODE_READWRITE)) !=
             (fptr->mode & FMODE_READWRITE)) {
@@ -6375,7 +6385,9 @@ rb_io_reopen(int argc, VALUE *argv, VALUE file)
                     rb_io_fmode_modestr(fmode));
        }
        fptr->mode = fmode;
-       rb_io_mode_enc(fptr, StringValueCStr(nmode));
+       if (NIL_P(intmode)) {
+           rb_io_mode_enc(fptr, StringValueCStr(nmode));
+       }
         fptr->encs.ecflags = 0;
         fptr->encs.ecopts = Qnil;
     }
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index e266f11..75ac744 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -1713,6 +1713,24 @@ End
     }
   end

+  def test_reopen_mode
+    make_tempfile {|t|
+      open(__FILE__) do |f|
+        assert_nothing_raised {
+          f.reopen(t.path, "r")
+          assert_equal("foo\n", f.gets)
+        }
+      end
+
+      open(__FILE__) do |f|
+        assert_nothing_raised {
+          f.reopen(t.path, File::RDONLY)
+          assert_equal("foo\n", f.gets)
+        }
+      end
+    }
+  end
+
   def test_foreach
     a = []
     IO.foreach("|" + EnvUtil.rubybin + " -e 'puts :foo; puts :bar; puts :baz'") {|x| a << x }