diff --git a/mrbgems/mruby-io/mrblib/io.rb b/mrbgems/mruby-io/mrblib/io.rb
index 5f62784b9..986e7136f 100644
--- a/mrbgems/mruby-io/mrblib/io.rb
+++ b/mrbgems/mruby-io/mrblib/io.rb
@@ -86,17 +86,6 @@ class IO
     self.__id__
   end
 
-  def write(string)
-    str = string.is_a?(String) ? string : string.to_s
-    return 0 if str.empty?
-    unless @buf.empty?
-      # reset real pos ignore buf
-      seek(pos, SEEK_SET)
-    end
-    len = syswrite(str)
-    len
-  end
-
   def <<(str)
     write(str)
     self
diff --git a/mrbgems/mruby-io/src/io.c b/mrbgems/mruby-io/src/io.c
index 9d2fa67f1..ce3d25f81 100644
--- a/mrbgems/mruby-io/src/io.c
+++ b/mrbgems/mruby-io/src/io.c
@@ -1414,8 +1414,8 @@ io_sync(mrb_state *mrb, mrb_value self)
 }
 
 #ifndef MRB_WITH_IO_PREAD_PWRITE
-# define mrb_io_pread   mrb_notimplement_m
-# define mrb_io_pwrite  mrb_notimplement_m
+# define io_pread   mrb_notimplement_m
+# define io_pwrite  mrb_notimplement_m
 #else
 static off_t
 value2off(mrb_state *mrb, mrb_value offv)
@@ -1537,6 +1537,22 @@ io_readchar(mrb_state *mrb, mrb_value self)
   return io_bufread(mrb, buf, len);
 }
 
+  /* def write(string) */
+  /*   str = string.is_a?(String) ? string : string.to_s */
+  /*   return 0 if str.empty? */
+  /*   unless @buf.empty? */
+  /*     # reset real pos ignore buf */
+  /*     seek(pos, SEEK_SET) */
+  /*   end */
+  /*   len = syswrite(str) */
+  /*   len */
+  /* end */
+
+static mrb_value
+io_write(mrb_state *mrb, mrb_value self)
+{
+}
+
 void
 mrb_init_io(mrb_state *mrb)
 {
@@ -1571,6 +1587,7 @@ mrb_init_io(mrb_state *mrb)
   mrb_define_method(mrb, io, "closed?",    io_closed,     MRB_ARGS_NONE());   /* 15.2.20.5.2 */
   mrb_define_method(mrb, io, "pid",        io_pid,        MRB_ARGS_NONE());   /* 15.2.20.5.2 */
   mrb_define_method(mrb, io, "fileno",     io_fileno,     MRB_ARGS_NONE());
+  mrb_define_method(mrb, io, "write",      io_write,      MRB_ARGS_ANY());
   mrb_define_method(mrb, io, "pread",      io_pread,      MRB_ARGS_ANY());    /* ruby 2.5 feature */
   mrb_define_method(mrb, io, "pwrite",     io_pwrite,     MRB_ARGS_ANY());    /* ruby 2.5 feature */