diff --git a/ext/msgpack/unpacker.c b/ext/msgpack/unpacker.c
index 5024cd50..b2651cb0 100644
--- a/ext/msgpack/unpacker.c
+++ b/ext/msgpack/unpacker.c
@@ -211,7 +211,7 @@ static inline int object_complete(msgpack_unpacker_t* uk, VALUE object)
     return PRIMITIVE_OBJECT_COMPLETE;
 }
 
-static inline int object_complete_symbol(msgpack_unpacker_t* uk, VALUE object)
+static inline int object_complete_frozen(msgpack_unpacker_t* uk, VALUE object)
 {
     uk->last_object = object;
     reset_head_byte(uk);
@@ -222,9 +222,9 @@ static inline int object_complete_ext(msgpack_unpacker_t* uk, int ext_type, VALU
 {
     if (uk->optimized_symbol_ext_type && ext_type == uk->symbol_ext_type) {
         if (RB_UNLIKELY(NIL_P(str))) { // empty extension is returned as Qnil
-            return object_complete_symbol(uk, ID2SYM(rb_intern3("", 0, rb_utf8_encoding())));
+            return object_complete_frozen(uk, ID2SYM(rb_intern3("", 0, rb_utf8_encoding())));
         }
-        return object_complete_symbol(uk, rb_str_intern(str));
+        return object_complete_frozen(uk, rb_str_intern(str));
     }
 
     int ext_flags;
@@ -398,7 +398,7 @@ static inline int read_raw_body_begin(msgpack_unpacker_t* uk, int raw_type)
         int ret;
         if ((uk->optimized_symbol_ext_type && uk->symbol_ext_type == raw_type)) {
             VALUE symbol = msgpack_buffer_read_top_as_symbol(UNPACKER_BUFFER_(uk), length, raw_type != RAW_TYPE_BINARY);
-            ret = object_complete_symbol(uk, symbol);
+            ret = object_complete_frozen(uk, symbol);
         } else if (is_reading_map_key(uk) && raw_type == RAW_TYPE_STRING) {
            /* don't use zerocopy for hash keys but get a frozen string directly
             * because rb_hash_aset freezes keys and it causes copying */
@@ -409,7 +409,7 @@ static inline int read_raw_body_begin(msgpack_unpacker_t* uk, int raw_type)
                 } else {
                     key = msgpack_buffer_read_top_as_symbol(UNPACKER_BUFFER_(uk), length, true);
                 }
-                ret = object_complete_symbol(uk, key);
+                ret = object_complete_frozen(uk, key);
             } else {
                 if (uk->use_key_cache) {
                     key = msgpack_buffer_read_top_as_interned_string(UNPACKER_BUFFER_(uk), &uk->key_cache, length);
@@ -450,10 +450,10 @@ static int read_primitive(msgpack_unpacker_t* uk)
 
     SWITCH_RANGE_BEGIN(b)
     SWITCH_RANGE(b, 0x00, 0x7f)  // Positive Fixnum
-        return object_complete(uk, INT2NUM(b));
+        return object_complete_frozen(uk, INT2NUM(b));
 
     SWITCH_RANGE(b, 0xe0, 0xff)  // Negative Fixnum
-        return object_complete(uk, INT2NUM((int8_t)b));
+        return object_complete_frozen(uk, INT2NUM((int8_t)b));
 
     SWITCH_RANGE(b, 0xa0, 0xbf)  // FixRaw / fixstr
         size_t count = b & 0x1f;
@@ -478,15 +478,15 @@ static int read_primitive(msgpack_unpacker_t* uk)
     SWITCH_RANGE(b, 0xc0, 0xdf)  // Variable
         switch(b) {
         case 0xc0:  // nil
-            return object_complete(uk, Qnil);
+            return object_complete_frozen(uk, Qnil);
 
         //case 0xc1:  // string
 
         case 0xc2:  // false
-            return object_complete(uk, Qfalse);
+            return object_complete_frozen(uk, Qfalse);
 
         case 0xc3:  // true
-            return object_complete(uk, Qtrue);
+            return object_complete_frozen(uk, Qtrue);
 
         case 0xc7: // ext 8
             {
@@ -542,14 +542,14 @@ static int read_primitive(msgpack_unpacker_t* uk)
             {
                 READ_CAST_BLOCK_OR_RETURN_EOF(cb, uk, 1);
                 uint8_t u8 = cb.u8;
-                return object_complete(uk, INT2NUM((int)u8));
+                return object_complete_frozen(uk, INT2NUM((int)u8));
             }
 
         case 0xcd:  // unsigned int 16
             {
                 READ_CAST_BLOCK_OR_RETURN_EOF(cb, uk, 2);
                 uint16_t u16 = _msgpack_be16(cb.u16);
-                return object_complete(uk, INT2NUM((int)u16));
+                return object_complete_frozen(uk, INT2NUM((int)u16));
             }
 
         case 0xce:  // unsigned int 32
@@ -570,14 +570,14 @@ static int read_primitive(msgpack_unpacker_t* uk)
             {
                 READ_CAST_BLOCK_OR_RETURN_EOF(cb, uk, 1);
                 int8_t i8 = cb.i8;
-                return object_complete(uk, INT2NUM((int)i8));
+                return object_complete_frozen(uk, INT2NUM((int)i8));
             }
 
         case 0xd1:  // signed int 16
             {
                 READ_CAST_BLOCK_OR_RETURN_EOF(cb, uk, 2);
                 int16_t i16 = _msgpack_be16(cb.i16);
-                return object_complete(uk, INT2NUM((int)i16));
+                return object_complete_frozen(uk, INT2NUM((int)i16));
             }
 
         case 0xd2:  // signed int 32