diff --git a/mrbgems/mruby-bin-mrbc/tools/mrbc/mrbc.c b/mrbgems/mruby-bin-mrbc/tools/mrbc/mrbc.c
index 35ddec04e..550ebc0c7 100644
--- a/mrbgems/mruby-bin-mrbc/tools/mrbc/mrbc.c
+++ b/mrbgems/mruby-bin-mrbc/tools/mrbc/mrbc.c
@@ -26,7 +26,7 @@ struct mrbc_args {
   mrb_bool verbose      : 1;
   mrb_bool no_ext_ops   : 1;
   mrb_bool no_optimize  : 1;
-  uint8_t flags         : 2;
+  uint8_t flags         : 3;
 };
 
 static void