1 files changed, 2 insertions, 0 deletions
diff --git a/include/ruby/io.h b/include/ruby/io.h
index becf262eca..c2e0eaa2fc 100644
--- a/include/ruby/io.h
+++ b/include/ruby/io.h
@@ -45,6 +45,7 @@ typedef struct rb_io_t {
     int rbuf_off;
     int rbuf_len;
     int rbuf_capa;
+    VALUE tied_io_for_writing;
     rb_encoding *enc;
 } rb_io_t;
 
@@ -88,6 +89,7 @@ typedef struct rb_io_t {
     fp->rbuf_off = 0;\
     fp->rbuf_len = 0;\
     fp->rbuf_capa = 0;\
+    fp->tied_io_for_writing = 0;\
 } while (0)
 
 FILE *rb_io_stdio_file(rb_io_t *fptr);