diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index 878c500e..4651ff35 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -487,12 +487,6 @@ gc_mark_object(pic_state *pic, struct pic_object *obj)
     }
     break;
   }
-  case PIC_TT_BOX: {
-    struct pic_box *box = (struct pic_box *)obj;
-
-    gc_mark(pic, box->value);
-    break;
-  }
   case PIC_TT_NIL:
   case PIC_TT_BOOL:
 #if PIC_ENABLE_FLOAT
@@ -739,9 +733,6 @@ gc_finalize_object(pic_state *pic, struct pic_object *obj)
   case PIC_TT_CP: {
     break;
   }
-  case PIC_TT_BOX: {
-    break;
-  }
   case PIC_TT_NIL:
   case PIC_TT_BOOL:
 #if PIC_ENABLE_FLOAT
diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index 67b6f091..82429713 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -269,7 +269,6 @@ pic_value pic_fdisplay(pic_state *, pic_value, xFILE *);
 #include "picrin/symbol.h"
 #include "picrin/vector.h"
 #include "picrin/reg.h"
-#include "picrin/box.h"
 
 #if defined(__cplusplus)
 }
diff --git a/extlib/benz/include/picrin/box.h b/extlib/benz/include/picrin/box.h
deleted file mode 100644
index edce0f0d..00000000
--- a/extlib/benz/include/picrin/box.h
+++ /dev/null
@@ -1,53 +0,0 @@
-/**
- * See Copyright Notice in picrin.h
- */
-
-#ifndef PICRIN_BOX_H
-#define PICRIN_BOX_H
-
-#if defined(__cplusplus)
-extern "C" {
-#endif
-
-struct pic_box {
-  PIC_OBJECT_HEADER
-  pic_value value;
-};
-
-#define pic_box_p(v) (pic_type(v) == PIC_TT_BOX)
-#define pic_box_ptr(o) ((struct pic_box *)pic_ptr(o))
-
-PIC_INLINE pic_value
-pic_box(pic_state *pic, pic_value value)
-{
-  struct pic_box *box;
-
-  box = (struct pic_box *)pic_obj_alloc(pic, sizeof(struct pic_box), PIC_TT_BOX);
-  box->value = value;
-
-  return pic_obj_value(box);
-}
-
-PIC_INLINE pic_value
-pic_unbox(pic_state *pic, pic_value box)
-{
-  if (! pic_box_p(box)) {
-    pic_errorf(pic, "box required");
-  }
-  return pic_box_ptr(box)->value;
-}
-
-PIC_INLINE void
-pic_set_box(pic_state *pic, pic_value box, pic_value value)
-{
-  if (! pic_box_p(box)) {
-    pic_errorf(pic, "box required");
-  }
-  pic_box_ptr(box)->value = value;
-}
-
-#if defined(__cplusplus)
-}
-#endif
-
-#endif
diff --git a/extlib/benz/include/picrin/type.h b/extlib/benz/include/picrin/type.h
index c5d5f4da..e824d9b1 100644
--- a/extlib/benz/include/picrin/type.h
+++ b/extlib/benz/include/picrin/type.h
@@ -163,11 +163,10 @@ enum pic_tt {
   PIC_TT_DATA,
   PIC_TT_DICT,
   PIC_TT_REG,
-  PIC_TT_BOX,
   PIC_TT_RECORD,
   PIC_TT_CXT,
   PIC_TT_IREP,
-  PIC_TT_CP,
+  PIC_TT_CP
 };
 
 #define PIC_OBJECT_HEADER			\
@@ -338,8 +337,6 @@ pic_type_repr(enum pic_tt tt)
     return "reg";
   case PIC_TT_RECORD:
     return "record";
-  case PIC_TT_BOX:
-    return "box";
   case PIC_TT_CP:
     return "checkpoint";
   }