diff --git a/include/mruby.h b/include/mruby.h
index 7e2d2575f..0acd20842 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -60,9 +60,7 @@ enum mrb_vtype {
   MRB_TT_FILE,        /*  21 */
   MRB_TT_ENV,         /*  22 */
   MRB_TT_DATA,        /*  23 */
-  MRB_TT_THREAD,      /*  24 */
-  MRB_TT_THREADGRP,   /*  25 */
-  MRB_TT_MAXDEFINE    /*  26 */
+  MRB_TT_MAXDEFINE    /*  24 */
 };
 
 typedef struct mrb_value {
diff --git a/src/etc.c b/src/etc.c
index 10aba12a0..73cf31087 100644
--- a/src/etc.c
+++ b/src/etc.c
@@ -183,8 +183,6 @@ mrb_obj_id(mrb_value obj)
   case  MRB_TT_MATCH:
   case  MRB_TT_FILE:
   case  MRB_TT_DATA:
-  case  MRB_TT_THREAD:
-  case  MRB_TT_THREADGRP:
   default:
     return MakeID(obj.value.p);
   }