1 files changed, 1 insertions, 1 deletions
diff --git a/src/io.c b/src/io.c
index 2a24b18a4..f15f182f2 100644
--- a/src/io.c
+++ b/src/io.c
@@ -636,7 +636,7 @@ mrb_io_sysread(mrb_state *mrb, mrb_value io)
     buf = mrb_str_resize(mrb, buf, maxlen);
   }
 
-  fptr = (struct mrb_io *)mrb_get_datatype(mrb, io, &mrb_io_type);
+  fptr = (struct mrb_io *)io_get_open_fptr(mrb, io);
   ret = read(fptr->fd, RSTRING_PTR(buf), maxlen);
   switch (ret) {
     case 0: /* EOF */