diff --git a/ext/oj/cache.c b/ext/oj/cache.c
index ddbbafd6..5669b676 100644
--- a/ext/oj/cache.c
+++ b/ext/oj/cache.c
@@ -260,7 +260,8 @@ void cache_set_expunge_rate(Cache c, int rate) {
     c->xrate = (uint8_t)rate;
 }
 
-void cache_free(Cache c) {
+void cache_free(void *data) {
+    Cache    c = (Cache)data;
     uint64_t i;
 
     for (i = 0; i < c->size; i++) {
@@ -276,7 +277,8 @@ void cache_free(Cache c) {
     OJ_FREE(c);
 }
 
-void cache_mark(Cache c) {
+void cache_mark(void *data) {
+    Cache    c = (Cache)data;
     uint64_t i;
 
 #if !HAVE_PTHREAD_MUTEX_INIT
diff --git a/ext/oj/cache.h b/ext/oj/cache.h
index 84579a70..d372b69a 100644
--- a/ext/oj/cache.h
+++ b/ext/oj/cache.h
@@ -10,10 +10,11 @@
 #define CACHE_MAX_KEY 35
 
 struct _cache;
+typedef struct _cache *Cache;
 
 extern struct _cache *cache_create(size_t size, VALUE (*form)(const char *str, size_t len), bool mark, bool locking);
-extern void           cache_free(struct _cache *c);
-extern void           cache_mark(struct _cache *c);
+extern void           cache_free(void *data);
+extern void           cache_mark(void *data);
 extern void           cache_set_form(struct _cache *c, VALUE (*form)(const char *str, size_t len));
 extern VALUE          cache_intern(struct _cache *c, const char *key, size_t len);
 extern void           cache_set_expunge_rate(struct _cache *c, int rate);
diff --git a/ext/oj/dump.c b/ext/oj/dump.c
index 1a6d813d..1f5bfbe9 100644
--- a/ext/oj/dump.c
+++ b/ext/oj/dump.c
@@ -727,8 +727,11 @@ static void debug_raise(const char *orig, size_t cnt, int line) {
 
 void oj_dump_raw_json(VALUE obj, int depth, Out out) {
     if (oj_string_writer_class == rb_obj_class(obj)) {
-        StrWriter sw  = (StrWriter)DATA_PTR(obj);
-        size_t    len = sw->out.cur - sw->out.buf;
+        StrWriter sw;
+        size_t    len;
+
+        sw  = oj_str_writer_unwrap(obj);
+        len = sw->out.cur - sw->out.buf;
 
         if (0 < len) {
             len--;
diff --git a/ext/oj/fast.c b/ext/oj/fast.c
index ee53716d..841e0d50 100644
--- a/ext/oj/fast.c
+++ b/ext/oj/fast.c
@@ -780,11 +780,10 @@ static VALUE parse_json(VALUE clas, char *json, bool given) {
         }
     }
 #endif
-    doc->json           = json;
-    self                = TypedData_Wrap_Struct(clas, &oj_doc_type, doc);
-    doc->self           = self;
-    DATA_PTR(doc->self) = doc;
-    result              = rb_protect(protect_open_proc, (VALUE)&pi, &ex);
+    doc->json = json;
+    self      = TypedData_Wrap_Struct(clas, &oj_doc_type, doc);
+    doc->self = self;
+    result    = rb_protect(protect_open_proc, (VALUE)&pi, &ex);
     if (given || 0 != ex) {
         DATA_PTR(doc->self) = NULL;
         // TBD is this needed?
@@ -1609,7 +1608,9 @@ static VALUE doc_dump(int argc, VALUE *argv, VALUE self) {
  *   Oj::Doc.open('[1,2,3]') { |doc| doc.size() }  #=> 4
  */
 static VALUE doc_size(VALUE self) {
-    return ULONG2NUM(((Doc)DATA_PTR(self))->size);
+    Doc d;
+    TypedData_Get_Struct(self, struct _doc, &oj_doc_type, d);
+    return ULONG2NUM(d->size);
 }
 
 /* @overload close() => nil
diff --git a/ext/oj/intern.c b/ext/oj/intern.c
index 075bd1c3..ea12ebce 100644
--- a/ext/oj/intern.c
+++ b/ext/oj/intern.c
@@ -85,20 +85,31 @@ static VALUE form_attr(const char *str, size_t len) {
     return (VALUE)rb_intern3(buf, len + 1, oj_utf8_encoding);
 }
 
+static const rb_data_type_t oj_cache_type = {
+    "Oj/cache",
+    {
+        cache_mark,
+        cache_free,
+        NULL,
+    },
+    0,
+    0,
+};
+
 void oj_hash_init(void) {
     VALUE cache_class = rb_define_class_under(Oj, "Cache", rb_cObject);
     rb_undef_alloc_func(cache_class);
 
     struct _cache *str_cache = cache_create(0, form_str, true, true);
-    str_cache_obj            = Data_Wrap_Struct(cache_class, cache_mark, cache_free, str_cache);
+    str_cache_obj            = TypedData_Wrap_Struct(cache_class, &oj_cache_type, str_cache);
     rb_gc_register_address(&str_cache_obj);
 
     struct _cache *sym_cache = cache_create(0, form_sym, true, true);
-    sym_cache_obj            = Data_Wrap_Struct(cache_class, cache_mark, cache_free, sym_cache);
+    sym_cache_obj            = TypedData_Wrap_Struct(cache_class, &oj_cache_type, sym_cache);
     rb_gc_register_address(&sym_cache_obj);
 
     struct _cache *attr_cache = cache_create(0, form_attr, false, true);
-    attr_cache_obj            = Data_Wrap_Struct(cache_class, cache_mark, cache_free, attr_cache);
+    attr_cache_obj            = TypedData_Wrap_Struct(cache_class, &oj_cache_type, attr_cache);
     rb_gc_register_address(&attr_cache_obj);
 
     memset(class_hash.slots, 0, sizeof(class_hash.slots));
@@ -118,17 +129,23 @@ oj_str_intern(const char *key, size_t len) {
 #if HAVE_RB_ENC_INTERNED_STR && 0
     return rb_enc_interned_str(key, len, rb_utf8_encoding());
 #else
-    return cache_intern(DATA_PTR(str_cache_obj), key, len);
+    Cache c;
+    TypedData_Get_Struct(str_cache_obj, struct _cache, &oj_cache_type, c);
+    return cache_intern(c, key, len);
 #endif
 }
 
 VALUE
 oj_sym_intern(const char *key, size_t len) {
-    return cache_intern(DATA_PTR(sym_cache_obj), key, len);
+    Cache c;
+    TypedData_Get_Struct(sym_cache_obj, struct _cache, &oj_cache_type, c);
+    return cache_intern(c, key, len);
 }
 
 ID oj_attr_intern(const char *key, size_t len) {
-    return cache_intern(DATA_PTR(attr_cache_obj), key, len);
+    Cache c;
+    TypedData_Get_Struct(attr_cache_obj, struct _cache, &oj_cache_type, c);
+    return cache_intern(c, key, len);
 }
 
 static uint64_t hash_calc(const uint8_t *key, size_t len) {
diff --git a/ext/oj/oj.h b/ext/oj/oj.h
index b7a9934f..2d9b96e2 100644
--- a/ext/oj/oj.h
+++ b/ext/oj/oj.h
@@ -262,6 +262,8 @@ extern void  oj_dump_leaf_to_json(Leaf leaf, Options copts, Out out);
 extern void  oj_write_leaf_to_file(Leaf leaf, const char *path, Options copts);
 extern char *oj_longlong_to_string(long long num, bool negative, char *buf);
 
+extern StrWriter oj_str_writer_unwrap(VALUE writer);
+
 extern void oj_str_writer_push_key(StrWriter sw, const char *key);
 extern void oj_str_writer_push_object(StrWriter sw, const char *key);
 extern void oj_str_writer_push_array(StrWriter sw, const char *key);
diff --git a/ext/oj/parser.c b/ext/oj/parser.c
index 02ce2151..2ad234a4 100644
--- a/ext/oj/parser.c
+++ b/ext/oj/parser.c
@@ -1164,6 +1164,17 @@ static void parser_mark(void *ptr) {
     }
 }
 
+static const rb_data_type_t oj_parser_type = {
+    "Oj/parser",
+    {
+        parser_mark,
+        parser_free,
+        NULL,
+    },
+    0,
+    0,
+};
+
 extern void oj_set_parser_validator(ojParser p);
 extern void oj_set_parser_saj(ojParser p);
 extern void oj_set_parser_usual(ojParser p);
@@ -1255,7 +1266,7 @@ static VALUE parser_new(int argc, VALUE *argv, VALUE self) {
             rb_hash_foreach(ropts, opt_cb, (VALUE)p);
         }
     }
-    return Data_Wrap_Struct(parser_class, parser_mark, parser_free, p);
+    return TypedData_Wrap_Struct(parser_class, &oj_parser_type, p);
 }
 
 // Create a new parser without setting the delegate. The parser is
@@ -1275,7 +1286,7 @@ VALUE oj_parser_new(void) {
     buf_init(&p->buf);
     p->map = value_map;
 
-    return Data_Wrap_Struct(parser_class, parser_mark, parser_free, p);
+    return TypedData_Wrap_Struct(parser_class, &oj_parser_type, p);
 }
 
 // Set set the options from a hash (ropts).
@@ -1322,11 +1333,13 @@ void oj_parser_set_option(ojParser p, VALUE ropts) {
  *   - _symbol_keys_ is a flag that indicates Hash keys should be parsed to Symbols versus Strings.
  */
 static VALUE parser_missing(int argc, VALUE *argv, VALUE self) {
-    ojParser       p    = (ojParser)DATA_PTR(self);
+    ojParser       p;
     const char    *key  = NULL;
     volatile VALUE rkey = *argv;
     volatile VALUE rv   = Qnil;
 
+    TypedData_Get_Struct(self, struct _ojParser, &oj_parser_type, p);
+
 #if HAVE_RB_EXT_RACTOR_SAFE
     // This doesn't seem to do anything.
     rb_ext_ractor_safe(true);
@@ -1352,9 +1365,11 @@ static VALUE parser_missing(int argc, VALUE *argv, VALUE self) {
  * Returns the result according to the delegate of the parser.
  */
 static VALUE parser_parse(VALUE self, VALUE json) {
-    ojParser    p   = (ojParser)DATA_PTR(self);
+    ojParser    p;
     const byte *ptr = (const byte *)StringValuePtr(json);
 
+    TypedData_Get_Struct(self, struct _ojParser, &oj_parser_type, p);
+
     parser_reset(p);
     p->start(p);
     parse(p, ptr);
@@ -1368,9 +1383,11 @@ static VALUE load_rescue(VALUE self, VALUE x) {
 }
 
 static VALUE load(VALUE self) {
-    ojParser       p    = (ojParser)DATA_PTR(self);
+    ojParser       p;
     volatile VALUE rbuf = rb_str_new2("");
 
+    TypedData_Get_Struct(self, struct _ojParser, &oj_parser_type, p);
+
     p->start(p);
     while (true) {
         rb_funcall(p->reader, oj_readpartial_id, 2, INT2NUM(16385), rbuf);
@@ -1389,7 +1406,9 @@ static VALUE load(VALUE self) {
  * Returns the result according to the delegate of the parser.
  */
 static VALUE parser_load(VALUE self, VALUE reader) {
-    ojParser p = (ojParser)DATA_PTR(self);
+    ojParser p;
+
+    TypedData_Get_Struct(self, struct _ojParser, &oj_parser_type, p);
 
     parser_reset(p);
     p->reader = reader;
@@ -1406,10 +1425,12 @@ static VALUE parser_load(VALUE self, VALUE reader) {
  * Returns the result according to the delegate of the parser.
  */
 static VALUE parser_file(VALUE self, VALUE filename) {
-    ojParser    p = (ojParser)DATA_PTR(self);
+    ojParser    p;
     const char *path;
     int         fd;
 
+    TypedData_Get_Struct(self, struct _ojParser, &oj_parser_type, p);
+
     path = StringValuePtr(filename);
 
     parser_reset(p);
@@ -1453,7 +1474,9 @@ static VALUE parser_file(VALUE self, VALUE filename) {
  * Returns the current state of the just_one [_Boolean_] option.
  */
 static VALUE parser_just_one(VALUE self) {
-    ojParser p = (ojParser)DATA_PTR(self);
+    ojParser p;
+
+    TypedData_Get_Struct(self, struct _ojParser, &oj_parser_type, p);
 
     return p->just_one ? Qtrue : Qfalse;
 }
@@ -1467,7 +1490,9 @@ static VALUE parser_just_one(VALUE self) {
  * Returns the current state of the just_one [_Boolean_] option.
  */
 static VALUE parser_just_one_set(VALUE self, VALUE v) {
-    ojParser p = (ojParser)DATA_PTR(self);
+    ojParser p;
+
+    TypedData_Get_Struct(self, struct _ojParser, &oj_parser_type, p);
 
     p->just_one = (Qtrue == v);
 
@@ -1491,7 +1516,7 @@ static VALUE parser_usual(VALUE self) {
         buf_init(&p->buf);
         p->map = value_map;
         oj_set_parser_usual(p);
-        usual_parser = Data_Wrap_Struct(parser_class, parser_mark, parser_free, p);
+        usual_parser = TypedData_Wrap_Struct(parser_class, &oj_parser_type, p);
         rb_gc_register_address(&usual_parser);
     }
     return usual_parser;
@@ -1514,7 +1539,7 @@ static VALUE parser_saj(VALUE self) {
         buf_init(&p->buf);
         p->map = value_map;
         oj_set_parser_saj(p);
-        saj_parser = Data_Wrap_Struct(parser_class, parser_mark, parser_free, p);
+        saj_parser = TypedData_Wrap_Struct(parser_class, &oj_parser_type, p);
         rb_gc_register_address(&saj_parser);
     }
     return saj_parser;
@@ -1536,7 +1561,7 @@ static VALUE parser_validate(VALUE self) {
         buf_init(&p->buf);
         p->map = value_map;
         oj_set_parser_validator(p);
-        validate_parser = Data_Wrap_Struct(parser_class, parser_mark, parser_free, p);
+        validate_parser = TypedData_Wrap_Struct(parser_class, &oj_parser_type, p);
         rb_gc_register_address(&validate_parser);
     }
     return validate_parser;
diff --git a/ext/oj/rails.c b/ext/oj/rails.c
index fa48cc8b..91fed0db 100644
--- a/ext/oj/rails.c
+++ b/ext/oj/rails.c
@@ -639,6 +639,17 @@ static void encoder_mark(void *ptr) {
     }
 }
 
+static const rb_data_type_t oj_encoder_type = {
+    "Oj/encoder",
+    {
+        encoder_mark,
+        encoder_free,
+        NULL,
+    },
+    0,
+    0,
+};
+
 /* Document-method: new
  *	call-seq: new(options=nil)
  *
@@ -656,7 +667,7 @@ static VALUE encoder_new(int argc, VALUE *argv, VALUE self) {
         oj_parse_options(*argv, &e->opts);
         e->arg = *argv;
     }
-    return Data_Wrap_Struct(encoder_class, encoder_mark, encoder_free, e);
+    return TypedData_Wrap_Struct(encoder_class, &oj_encoder_type, e);
 }
 
 static VALUE resolve_classpath(const char *name) {
@@ -748,7 +759,8 @@ static void optimize(int argc, VALUE *argv, ROptTable rot, bool on) {
  * - *classes* [_Class_] a list of classes to optimize
  */
 static VALUE encoder_optimize(int argc, VALUE *argv, VALUE self) {
-    Encoder e = (Encoder)DATA_PTR(self);
+    Encoder e;
+    TypedData_Get_Struct(self, struct _encoder, &oj_encoder_type, e);
 
     optimize(argc, argv, &e->ropts, true);
 
@@ -804,7 +816,8 @@ rails_mimic_json(VALUE self) {
  * - *classes* [_Class_] a list of classes to deoptimize
  */
 static VALUE encoder_deoptimize(int argc, VALUE *argv, VALUE self) {
-    Encoder e = (Encoder)DATA_PTR(self);
+    Encoder e;
+    TypedData_Get_Struct(self, struct _encoder, &oj_encoder_type, e);
 
     optimize(argc, argv, &e->ropts, false);
 
@@ -833,8 +846,11 @@ static VALUE rails_deoptimize(int argc, VALUE *argv, VALUE self) {
  * @return true if the class is being optimized for rails and false otherwise
  */
 static VALUE encoder_optimized(VALUE self, VALUE clas) {
-    Encoder e  = (Encoder)DATA_PTR(self);
-    ROpt    ro = oj_rails_get_opt(&e->ropts, clas);
+    Encoder e;
+    ROpt    ro;
+
+    TypedData_Get_Struct(self, struct _encoder, &oj_encoder_type, e);
+    ro = oj_rails_get_opt(&e->ropts, clas);
 
     if (NULL == ro) {
         return Qfalse;
@@ -940,7 +956,8 @@ static VALUE encode(VALUE obj, ROptTable ropts, Options opts, int argc, VALUE *a
  * Returns encoded object as a JSON string.
  */
 static VALUE encoder_encode(VALUE self, VALUE obj) {
-    Encoder e = (Encoder)DATA_PTR(self);
+    Encoder e;
+    TypedData_Get_Struct(self, struct _encoder, &oj_encoder_type, e);
 
     if (Qnil != e->arg) {
         VALUE argv[1] = {e->arg};
diff --git a/ext/oj/stream_writer.c b/ext/oj/stream_writer.c
index decc705b..a1cff080 100644
--- a/ext/oj/stream_writer.c
+++ b/ext/oj/stream_writer.c
@@ -21,6 +21,17 @@ static void stream_writer_free(void *ptr) {
     OJ_R_FREE(ptr);
 }
 
+static const rb_data_type_t oj_stream_writer_type = {
+    "Oj/stream_writer",
+    {
+        NULL,
+        stream_writer_free,
+        NULL,
+    },
+    0,
+    0,
+};
+
 static void stream_writer_reset_buf(StreamWriter sw) {
     sw->sw.out.cur  = sw->sw.out.buf;
     *sw->sw.out.cur = '\0';
@@ -120,7 +131,7 @@ static VALUE stream_writer_new(int argc, VALUE *argv, VALUE self) {
     sw->type          = type;
     sw->fd            = fd;
 
-    return Data_Wrap_Struct(oj_stream_writer_class, 0, stream_writer_free, sw);
+    return TypedData_Wrap_Struct(oj_stream_writer_class, &oj_stream_writer_type, sw);
 }
 
 /* Document-method: push_key
@@ -133,7 +144,8 @@ static VALUE stream_writer_new(int argc, VALUE *argv, VALUE self) {
  * - *key* [_String_] the key pending for the next push
  */
 static VALUE stream_writer_push_key(VALUE self, VALUE key) {
-    StreamWriter sw = (StreamWriter)DATA_PTR(self);
+    StreamWriter sw;
+    TypedData_Get_Struct(self, struct _streamWriter, &oj_stream_writer_type, sw);
 
     oj_str_writer_push_key(&sw->sw, StringValuePtr(key));
     if (sw->flush_limit < sw->sw.out.cur - sw->sw.out.buf) {
@@ -151,7 +163,8 @@ static VALUE stream_writer_push_key(VALUE self, VALUE key) {
  * - *key* [_String_] the key if adding to an object in the JSON document
  */
 static VALUE stream_writer_push_object(int argc, VALUE *argv, VALUE self) {
-    StreamWriter sw = (StreamWriter)DATA_PTR(self);
+    StreamWriter sw;
+    TypedData_Get_Struct(self, struct _streamWriter, &oj_stream_writer_type, sw);
 
     switch (argc) {
     case 0: oj_str_writer_push_object(&sw->sw, 0); break;
@@ -179,7 +192,8 @@ static VALUE stream_writer_push_object(int argc, VALUE *argv, VALUE self) {
  * - *key* [_String_] the key if adding to an object in the JSON document
  */
 static VALUE stream_writer_push_array(int argc, VALUE *argv, VALUE self) {
-    StreamWriter sw = (StreamWriter)DATA_PTR(self);
+    StreamWriter sw;
+    TypedData_Get_Struct(self, struct _streamWriter, &oj_stream_writer_type, sw);
 
     switch (argc) {
     case 0: oj_str_writer_push_array(&sw->sw, 0); break;
@@ -206,15 +220,16 @@ static VALUE stream_writer_push_array(int argc, VALUE *argv, VALUE self) {
  * - *key* [_String_] the key if adding to an object in the JSON document
  */
 static VALUE stream_writer_push_value(int argc, VALUE *argv, VALUE self) {
-    StreamWriter sw = (StreamWriter)DATA_PTR(self);
+    StreamWriter sw;
+    TypedData_Get_Struct(self, struct _streamWriter, &oj_stream_writer_type, sw);
 
     switch (argc) {
-    case 1: oj_str_writer_push_value((StrWriter)DATA_PTR(self), *argv, 0); break;
+    case 1: oj_str_writer_push_value((StrWriter)sw, *argv, 0); break;
     case 2:
         if (Qnil == argv[1]) {
-            oj_str_writer_push_value((StrWriter)DATA_PTR(self), *argv, 0);
+            oj_str_writer_push_value((StrWriter)sw, *argv, 0);
         } else {
-            oj_str_writer_push_value((StrWriter)DATA_PTR(self), *argv, StringValuePtr(argv[1]));
+            oj_str_writer_push_value((StrWriter)sw, *argv, StringValuePtr(argv[1]));
         }
         break;
     default: rb_raise(rb_eArgError, "Wrong number of argument to 'push_value'."); break;
@@ -235,15 +250,16 @@ static VALUE stream_writer_push_value(int argc, VALUE *argv, VALUE self) {
  * - *key* [_String_] the key if adding to an object in the JSON document
  */
 static VALUE stream_writer_push_json(int argc, VALUE *argv, VALUE self) {
-    StreamWriter sw = (StreamWriter)DATA_PTR(self);
+    StreamWriter sw;
+    TypedData_Get_Struct(self, struct _streamWriter, &oj_stream_writer_type, sw);
 
     switch (argc) {
-    case 1: oj_str_writer_push_json((StrWriter)DATA_PTR(self), StringValuePtr(*argv), 0); break;
+    case 1: oj_str_writer_push_json((StrWriter)sw, StringValuePtr(*argv), 0); break;
     case 2:
         if (Qnil == argv[1]) {
-            oj_str_writer_push_json((StrWriter)DATA_PTR(self), StringValuePtr(*argv), 0);
+            oj_str_writer_push_json((StrWriter)sw, StringValuePtr(*argv), 0);
         } else {
-            oj_str_writer_push_json((StrWriter)DATA_PTR(self), StringValuePtr(*argv), StringValuePtr(argv[1]));
+            oj_str_writer_push_json((StrWriter)sw, StringValuePtr(*argv), StringValuePtr(argv[1]));
         }
         break;
     default: rb_raise(rb_eArgError, "Wrong number of argument to 'push_json'."); break;
@@ -261,7 +277,8 @@ static VALUE stream_writer_push_json(int argc, VALUE *argv, VALUE self) {
  * currently open.
  */
 static VALUE stream_writer_pop(VALUE self) {
-    StreamWriter sw = (StreamWriter)DATA_PTR(self);
+    StreamWriter sw;
+    TypedData_Get_Struct(self, struct _streamWriter, &oj_stream_writer_type, sw);
 
     oj_str_writer_pop(&sw->sw);
     if (sw->flush_limit < sw->sw.out.cur - sw->sw.out.buf) {
@@ -277,7 +294,8 @@ static VALUE stream_writer_pop(VALUE self) {
  * currently open.
  */
 static VALUE stream_writer_pop_all(VALUE self) {
-    StreamWriter sw = (StreamWriter)DATA_PTR(self);
+    StreamWriter sw;
+    TypedData_Get_Struct(self, struct _streamWriter, &oj_stream_writer_type, sw);
 
     oj_str_writer_pop_all(&sw->sw);
     stream_writer_write(sw);
@@ -291,7 +309,9 @@ static VALUE stream_writer_pop_all(VALUE self) {
  * Flush any remaining characters in the buffer.
  */
 static VALUE stream_writer_flush(VALUE self) {
-    stream_writer_write((StreamWriter)DATA_PTR(self));
+    StreamWriter sw;
+    TypedData_Get_Struct(self, struct _streamWriter, &oj_stream_writer_type, sw);
+    stream_writer_write(sw);
 
     return Qnil;
 }
diff --git a/ext/oj/string_writer.c b/ext/oj/string_writer.c
index 6f979482..cb5ff102 100644
--- a/ext/oj/string_writer.c
+++ b/ext/oj/string_writer.c
@@ -225,7 +225,7 @@ void oj_str_writer_pop_all(StrWriter sw) {
     }
 }
 
-static void str_writer_free(void *ptr) {
+static void string_writer_free(void *ptr) {
     StrWriter sw;
 
     if (0 == ptr) {
@@ -239,6 +239,23 @@ static void str_writer_free(void *ptr) {
     OJ_R_FREE(ptr);
 }
 
+static const rb_data_type_t oj_string_writer_type = {
+    "Oj/string_writer",
+    {
+        NULL,
+        string_writer_free,
+        NULL,
+    },
+    0,
+    0,
+};
+
+StrWriter oj_str_writer_unwrap(VALUE writer) {
+    StrWriter sw;
+    TypedData_Get_Struct(writer, struct _strWriter, &oj_string_writer_type, sw);
+    return sw;
+}
+
 /* Document-method: new
  * call-seq: new(io, options)
  *
@@ -266,7 +283,7 @@ static VALUE str_writer_new(int argc, VALUE *argv, VALUE self) {
     sw->out.argv   = argv + 1;
     sw->out.indent = sw->opts.indent;
 
-    return Data_Wrap_Struct(oj_string_writer_class, 0, str_writer_free, sw);
+    return TypedData_Wrap_Struct(oj_string_writer_class, &oj_string_writer_type, sw);
 }
 
 /* Document-method: push_key
@@ -278,7 +295,8 @@ static VALUE str_writer_new(int argc, VALUE *argv, VALUE self) {
  * - *key* [_String_] the key pending for the next push
  */
 static VALUE str_writer_push_key(VALUE self, VALUE key) {
-    StrWriter sw = (StrWriter)DATA_PTR(self);
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
 
     oj_str_writer_push_key(sw, StringValuePtr(key));
 
@@ -293,7 +311,8 @@ static VALUE str_writer_push_key(VALUE self, VALUE key) {
  * - *key* [_String_] the key if adding to an object in the JSON document
  */
 static VALUE str_writer_push_object(int argc, VALUE *argv, VALUE self) {
-    StrWriter sw = (StrWriter)DATA_PTR(self);
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
 
     switch (argc) {
     case 0: oj_str_writer_push_object(sw, 0); break;
@@ -321,7 +340,8 @@ static VALUE str_writer_push_object(int argc, VALUE *argv, VALUE self) {
  * - *key* [_String_] the key if adding to an object in the JSON document
  */
 static VALUE str_writer_push_array(int argc, VALUE *argv, VALUE self) {
-    StrWriter sw = (StrWriter)DATA_PTR(self);
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
 
     switch (argc) {
     case 0: oj_str_writer_push_array(sw, 0); break;
@@ -349,13 +369,16 @@ static VALUE str_writer_push_array(int argc, VALUE *argv, VALUE self) {
  * - *key* [_String_] the key if adding to an object in the JSON document
  */
 static VALUE str_writer_push_value(int argc, VALUE *argv, VALUE self) {
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
+
     switch (argc) {
-    case 1: oj_str_writer_push_value((StrWriter)DATA_PTR(self), *argv, 0); break;
+    case 1: oj_str_writer_push_value(sw, *argv, 0); break;
     case 2:
         if (Qnil == argv[1]) {
-            oj_str_writer_push_value((StrWriter)DATA_PTR(self), *argv, 0);
+            oj_str_writer_push_value(sw, *argv, 0);
         } else {
-            oj_str_writer_push_value((StrWriter)DATA_PTR(self), *argv, StringValuePtr(argv[1]));
+            oj_str_writer_push_value(sw, *argv, StringValuePtr(argv[1]));
         }
         break;
     default: rb_raise(rb_eArgError, "Wrong number of argument to 'push_value'."); break;
@@ -373,13 +396,16 @@ static VALUE str_writer_push_value(int argc, VALUE *argv, VALUE self) {
  * - *key* [_String_] the key if adding to an object in the JSON document
  */
 static VALUE str_writer_push_json(int argc, VALUE *argv, VALUE self) {
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
+
     switch (argc) {
-    case 1: oj_str_writer_push_json((StrWriter)DATA_PTR(self), StringValuePtr(*argv), 0); break;
+    case 1: oj_str_writer_push_json(sw, StringValuePtr(*argv), 0); break;
     case 2:
         if (Qnil == argv[1]) {
-            oj_str_writer_push_json((StrWriter)DATA_PTR(self), StringValuePtr(*argv), 0);
+            oj_str_writer_push_json(sw, StringValuePtr(*argv), 0);
         } else {
-            oj_str_writer_push_json((StrWriter)DATA_PTR(self), StringValuePtr(*argv), StringValuePtr(argv[1]));
+            oj_str_writer_push_json(sw, StringValuePtr(*argv), StringValuePtr(argv[1]));
         }
         break;
     default: rb_raise(rb_eArgError, "Wrong number of argument to 'push_json'."); break;
@@ -393,7 +419,10 @@ static VALUE str_writer_push_json(int argc, VALUE *argv, VALUE self) {
  * currently open.
  */
 static VALUE str_writer_pop(VALUE self) {
-    oj_str_writer_pop((StrWriter)DATA_PTR(self));
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
+
+    oj_str_writer_pop(sw);
     return Qnil;
 }
 
@@ -404,7 +433,10 @@ static VALUE str_writer_pop(VALUE self) {
  * currently open.
  */
 static VALUE str_writer_pop_all(VALUE self) {
-    oj_str_writer_pop_all((StrWriter)DATA_PTR(self));
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
+
+    oj_str_writer_pop_all(sw);
 
     return Qnil;
 }
@@ -415,7 +447,8 @@ static VALUE str_writer_pop_all(VALUE self) {
  * Reset the writer back to the empty state.
  */
 static VALUE str_writer_reset(VALUE self) {
-    StrWriter sw = (StrWriter)DATA_PTR(self);
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
 
     sw->depth      = 0;
     *sw->types     = '\0';
@@ -434,8 +467,9 @@ static VALUE str_writer_reset(VALUE self) {
  * *return* [_String_]
  */
 static VALUE str_writer_to_s(VALUE self) {
-    StrWriter sw   = (StrWriter)DATA_PTR(self);
-    VALUE     rstr = rb_str_new(sw->out.buf, sw->out.cur - sw->out.buf);
+    StrWriter sw;
+    TypedData_Get_Struct(self, struct _strWriter, &oj_string_writer_type, sw);
+    VALUE rstr = rb_str_new(sw->out.buf, sw->out.cur - sw->out.buf);
 
     return oj_encode(rstr);
 }
diff --git a/ext/oj/val_stack.c b/ext/oj/val_stack.c
index eeaeaf94..b27d0f2e 100644
--- a/ext/oj/val_stack.c
+++ b/ext/oj/val_stack.c
@@ -8,7 +8,7 @@
 #include "odd.h"
 #include "oj.h"
 
-static void mark(void *ptr) {
+static void stack_mark(void *ptr) {
     ValStack stack = (ValStack)ptr;
     Val      v;
 
@@ -46,6 +46,17 @@ static void mark(void *ptr) {
 #endif
 }
 
+static const rb_data_type_t oj_stack_type = {
+    "Oj/stack",
+    {
+        stack_mark,
+        NULL,
+        NULL,
+    },
+    0,
+    0,
+};
+
 VALUE
 oj_stack_init(ValStack stack) {
 #ifdef HAVE_PTHREAD_MUTEX_INIT
@@ -70,7 +81,7 @@ oj_stack_init(ValStack stack) {
     stack->head->clen      = 0;
     stack->head->next      = NEXT_NONE;
 
-    return Data_Wrap_Struct(oj_cstack_class, mark, 0, stack);
+    return TypedData_Wrap_Struct(oj_cstack_class, &oj_stack_type, stack);
 }
 
 const char *oj_stack_next_string(ValNext n) {