diff --git a/include/mruby/boxing_nan.h b/include/mruby/boxing_nan.h
index f412568dd..d76759ab0 100644
--- a/include/mruby/boxing_nan.h
+++ b/include/mruby/boxing_nan.h
@@ -98,6 +98,16 @@ mrb_type(mrb_value o)
   }
 }
 
+MRB_INLINE enum mrb_vtype
+mrb_unboxed_type(mrb_value o)
+{
+  if (!mrb_float_p(o) && mrb_nb_tt(o) == MRB_NANBOX_TT_OBJECT && o.u != 0) {
+    return ((struct RBasic*)(uintptr_t)o.u)->tt;
+  } else {
+    return MRB_TT_FALSE;
+  }
+}
+
 #define NANBOX_SET_MISC_VALUE(r,t,i) NANBOX_SET_VALUE(r, MRB_NANBOX_TT_MISC, ((uint64_t)(t)<<32) | (i))
 
 #define mrb_float(o) mrb_nan_boxing_value_float(o)
diff --git a/include/mruby/boxing_no.h b/include/mruby/boxing_no.h
index 84908a0d8..e261e4d17 100644
--- a/include/mruby/boxing_no.h
+++ b/include/mruby/boxing_no.h
@@ -26,15 +26,16 @@ typedef struct mrb_value {
   enum mrb_vtype tt;
 } mrb_value;
 
-#define mrb_ptr(o)      (o).value.p
-#define mrb_cptr(o)     mrb_ptr(o)
+#define mrb_ptr(o)          (o).value.p
+#define mrb_cptr(o)         mrb_ptr(o)
 #ifndef MRB_NO_FLOAT
-#define mrb_float(o)    (o).value.f
+#define mrb_float(o)        (o).value.f
 #endif
-#define mrb_fixnum(o)   (o).value.i
-#define mrb_integer(o)  mrb_fixnum(o)
-#define mrb_symbol(o)   (o).value.sym
-#define mrb_type(o)     (o).tt
+#define mrb_fixnum(o)       (o).value.i
+#define mrb_integer(o)      mrb_fixnum(o)
+#define mrb_symbol(o)       (o).value.sym
+#define mrb_type(o)         (o).tt
+#define mrb_unboxed_type(o) (o).tt
 
 #define BOXNIX_SET_VALUE(o, ttt, attr, v) do {\
   (o).tt = ttt;\
diff --git a/include/mruby/boxing_word.h b/include/mruby/boxing_word.h
index d3ca18eb4..b39307e33 100644
--- a/include/mruby/boxing_word.h
+++ b/include/mruby/boxing_word.h
@@ -228,4 +228,17 @@ mrb_type(mrb_value o)
          mrb_val_union(o).bp->tt;
 }
 
+MRB_INLINE enum mrb_vtype
+mrb_unboxed_type(mrb_value o)
+{
+  if (mrb_nil_p(o)) {
+    return MRB_TT_FALSE;
+  } else if ((o.w & WORDBOX_IMMEDIATE_MASK) == 0) {
+    return mrb_val_union(o).bp->tt;
+  } else {
+    return MRB_TT_FALSE;
+  }
+}
+
+
 #endif  /* MRUBY_BOXING_WORD_H */
diff --git a/include/mruby/value.h b/include/mruby/value.h
index 16da2cbd4..96af28d35 100644
--- a/include/mruby/value.h
+++ b/include/mruby/value.h
@@ -143,16 +143,16 @@ static const unsigned int IEEE754_INFINITY_BITS_SINGLE = 0x7F800000;
   f(MRB_TT_OBJECT,      struct RObject,     "Object") \
   f(MRB_TT_CLASS,       struct RClass,      "Class") \
   f(MRB_TT_MODULE,      struct RClass,      "Module") \
-  f(MRB_TT_ICLASS,      struct RClass,      "iClass") \
   f(MRB_TT_SCLASS,      struct RClass,      "SClass") \
+  f(MRB_TT_HASH,        struct RHash,       "Hash") \
+  f(MRB_TT_CDATA,       struct RData,       "C data") \
+  f(MRB_TT_EXCEPTION,   struct RException,  "Exception") \
+  f(MRB_TT_ICLASS,      struct RClass,      "iClass") \
   f(MRB_TT_PROC,        struct RProc,       "Proc") \
   f(MRB_TT_ARRAY,       struct RArray,      "Array") \
-  f(MRB_TT_HASH,        struct RHash,       "Hash") \
   f(MRB_TT_STRING,      struct RString,     "String") \
   f(MRB_TT_RANGE,       struct RRange,      "Range") \
-  f(MRB_TT_EXCEPTION,   struct RException,  "Exception") \
   f(MRB_TT_ENV,         struct REnv,        "env") \
-  f(MRB_TT_CDATA,       struct RData,       "C data") \
   f(MRB_TT_FIBER,       struct RFiber,      "Fiber") \
   f(MRB_TT_STRUCT,      struct RArray,      "Struct") \
   f(MRB_TT_ISTRUCT,     struct RIStruct,    "istruct") \
diff --git a/src/variable.c b/src/variable.c
index 2afbfd93e..d224a5a34 100644
--- a/src/variable.c
+++ b/src/variable.c
@@ -282,7 +282,7 @@ mrb_vm_special_set(mrb_state *mrb, mrb_sym i, mrb_value v)
 static mrb_bool
 obj_iv_p(mrb_value obj)
 {
-  switch (mrb_type(obj)) {
+  switch (mrb_unboxed_type(obj)) {
     case MRB_TT_OBJECT:
     case MRB_TT_CLASS:
     case MRB_TT_MODULE: