diff --git a/mrbgems/mruby-io/src/io.c b/mrbgems/mruby-io/src/io.c
index 1767f66ba..6b506c4aa 100644
--- a/mrbgems/mruby-io/src/io.c
+++ b/mrbgems/mruby-io/src/io.c
@@ -522,8 +522,6 @@ io_s_popen(mrb_state *mrb, mrb_value klass)
   }
 
   if (!doexec) {
-    // XXX
-    fflush(stdin);
     fflush(stdout);
     fflush(stderr);
   }