diff --git a/io.c b/io.c
index d3c6392fa2..980f8232bf 100644
--- a/io.c
+++ b/io.c
@@ -7716,7 +7716,7 @@ rb_file_initialize(int argc, VALUE *argv, VALUE io)
 	rb_raise(rb_eRuntimeError, "reinitializing File");
     }
     if (0 < argc && argc < 3) {
-	VALUE fd = rb_check_convert_type(argv[0], T_FIXNUM, "Fixnum", "to_int");
+	VALUE fd = rb_check_to_int(argv[0]);
 
 	if (!NIL_P(fd)) {
 	    argv[0] = fd;