diff --git a/io.c b/io.c
index 14807ae1ee..df05436dde 100644
--- a/io.c
+++ b/io.c
@@ -281,6 +281,11 @@ rb_io_get_write_io(VALUE io)
  *
  *     IO.try_convert(STDOUT)     # => STDOUT
  *     IO.try_convert("STDOUT")   # => nil
+ *
+ *     f = open("/tmp/zz.gz")       # => #<File:/tmp/zz.gz>
+ *     z = Zlib::GzipReader.open(f) # => #<Zlib::GzipReader:0x81d8744>
+ *     IO.try_convert(z)            # => #<File:/tmp/zz.gz>
+ *
  */
 static VALUE
 rb_io_s_try_convert(VALUE dummy, VALUE io)