diff --git a/io.c b/io.c
index 92dc006..9ca7b83 100644
--- a/io.c
+++ b/io.c
@@ -6104,6 +6104,8 @@ rb_io_initialize(int argc, VALUE *argv, VALUE io)
 	fp->stdio_file = stdout;
     else if (fileno(stderr) == fd)
 	fp->stdio_file = stderr;
+    else
+	fp->stdio_file = rb_fdopen(fd, rb_io_oflags_modestr(oflags));
 
     return io;
 }