diff --git a/binding-mruby/binding-mruby.cpp b/binding-mruby/binding-mruby.cpp
index 1ccbf6e..ad092db 100644
--- a/binding-mruby/binding-mruby.cpp
+++ b/binding-mruby/binding-mruby.cpp
@@ -140,7 +140,7 @@ mkxpTimeOp(mrb_state *mrb, mrb_value)
 	printf("<%s> [%f ms]\n", opName, ms);
 	fflush(stdout);
 
-	return mrb__float_value(ms);
+	return mrb_float_value(mrb, ms);
 }
 
 static const char *
diff --git a/binding-mruby/binding-util.h b/binding-mruby/binding-util.h
index c6cefae..170e77b 100644
--- a/binding-mruby/binding-util.h
+++ b/binding-mruby/binding-util.h
@@ -112,6 +112,12 @@ getMrbData(mrb_state *mrb)
 	return static_cast<MrbData*>(mrb->ud);
 }
 
+inline RClass*
+defineClass(mrb_state *mrb, const char *name)
+{
+	return mrb_define_class(mrb, name, mrb->object_class);
+}
+
 #define GUARD_EXC(exp) \
 { try { exp } catch (Exception &exc) { raiseMrbExc(mrb, exc); } }
 
@@ -237,7 +243,7 @@ mrb__float_value(mrb_float f)
 {
 	mrb_value v;
 
-	MRB_SET_VALUE(v, MRB_TT_FLOAT, value.f, f);
+	SET_FLOAT_VALUE(0, v, f);
 	return v;
 }
 
diff --git a/binding-mruby/bitmap-binding.cpp b/binding-mruby/bitmap-binding.cpp
index 3a91efd..301ea29 100644
--- a/binding-mruby/bitmap-binding.cpp
+++ b/binding-mruby/bitmap-binding.cpp
@@ -306,7 +306,7 @@ CLONE_FUN(Bitmap)
 void
 bitmapBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "Bitmap", 0);
+	RClass *klass = defineClass(mrb, "Bitmap");
 
 	disposableBindingInit<Bitmap>(mrb, klass);
 
diff --git a/binding-mruby/etc-binding.cpp b/binding-mruby/etc-binding.cpp
index 6fae107..f65ed19 100644
--- a/binding-mruby/etc-binding.cpp
+++ b/binding-mruby/etc-binding.cpp
@@ -169,7 +169,7 @@ CLONE_FUN(Rect)
 
 #define INIT_BIND(Klass) \
 { \
-	klass = mrb_define_class(mrb, #Klass, 0); \
+	klass = defineClass(mrb, #Klass); \
 	mrb_define_class_method(mrb, klass, "_load", Klass##Load, MRB_ARGS_REQ(1)); \
 	serializableBindingInit<Klass>(mrb, klass); \
 	mrb_define_method(mrb, klass, "initialize", Klass##Initialize, MRB_ARGS_REQ(3) | MRB_ARGS_OPT(1)); \
diff --git a/binding-mruby/font-binding.cpp b/binding-mruby/font-binding.cpp
index 25477a0..c3c5afc 100644
--- a/binding-mruby/font-binding.cpp
+++ b/binding-mruby/font-binding.cpp
@@ -142,7 +142,7 @@ MRB_METHOD(FontSetDefaultColor)
 void
 fontBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "Font", 0);
+	RClass *klass = defineClass(mrb, "Font");
 
 	Font::setDefaultColor(new Color(*Font::getDefaultColor()));
 	wrapProperty(mrb, mrb_obj_value(klass), Font::getDefaultColor(), CSdefault_color, ColorType);
diff --git a/binding-mruby/mrb-ext/file.cpp b/binding-mruby/mrb-ext/file.cpp
index 845817e..b68bb7b 100644
--- a/binding-mruby/mrb-ext/file.cpp
+++ b/binding-mruby/mrb-ext/file.cpp
@@ -227,7 +227,7 @@ MRB_FUNCTION(fileExpandPath)
 	if (defDir)
 		Debug() << "FIXME: File.expand_path: default_dir not implemented";
 
-	char buffer[512];
+	char buffer[PATH_MAX];
 	char *unused = realpath(path, buffer);
 	(void) unused;
 
@@ -568,7 +568,7 @@ fileBindingInit(mrb_state *mrb)
 {
 	mrb_define_method(mrb, mrb->kernel_module, "open", fileOpen, MRB_ARGS_REQ(1) | MRB_ARGS_OPT(1) | MRB_ARGS_BLOCK());
 
-	RClass *klass = mrb_define_class(mrb, "IO", 0);
+	RClass *klass = defineClass(mrb, "IO");
 	klass = mrb_define_class(mrb, "File", klass);
 
 	mrb_define_class_method(mrb, klass, "basename", fileBasename, MRB_ARGS_REQ(1) | MRB_ARGS_OPT(1));
diff --git a/binding-mruby/mrb-ext/marshal.cpp b/binding-mruby/mrb-ext/marshal.cpp
index 385a22f..a64bf9a 100644
--- a/binding-mruby/mrb-ext/marshal.cpp
+++ b/binding-mruby/mrb-ext/marshal.cpp
@@ -259,21 +259,13 @@ read_string_value(MarshalContext *ctx)
 	mrb_state *mrb = ctx->mrb;
 	int len = read_fixnum(ctx);
 
-	struct RString *str =
-		(struct RString*) mrb_obj_alloc
-			(mrb, MRB_TT_STRING, mrb->string_class);
+	mrb_value str = mrb_str_new(mrb, 0, len);
+	char *ptr = RSTR_PTR(RSTRING(str));
 
-	str->c = mrb->string_class;
-	str->len = len;
-	str->aux.capa = len;
-	str->ptr = (char*) mrb_malloc(mrb, len+1);
+	ctx->readData(ptr, len);
+	ptr[len] = '\0';
 
-	ctx->readData(str->ptr, len);
-	str->ptr[len] = '\0';
-
-	mrb_value str_obj = mrb_obj_value(str);
-
-	return str_obj;
+	return str;
 }
 
 static mrb_value read_value(MarshalContext *ctx);
@@ -724,7 +716,7 @@ write_symbol(MarshalContext *ctx, mrb_value symbol)
 {
 	mrb_state *mrb = ctx->mrb;
 	mrb_sym sym = mrb_symbol(symbol);
-	size_t len;
+	mrb_int len;
 	const char *p = mrb_sym2name_len(mrb, sym, &len);
 
 	write_string(ctx, p);
diff --git a/binding-mruby/mrb-ext/time.cpp b/binding-mruby/mrb-ext/time.cpp
index b0ceead..e6b1557 100644
--- a/binding-mruby/mrb-ext/time.cpp
+++ b/binding-mruby/mrb-ext/time.cpp
@@ -197,8 +197,8 @@ TIME_ATTR(wday)
 void
 timeBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "Time", 0);
-	mrb_include_module(mrb, klass, mrb_class_get(mrb, "Comparable"));
+	RClass *klass = defineClass(mrb, "Time");
+	mrb_include_module(mrb, klass, mrb_module_get(mrb, "Comparable"));
 
 	mrb_define_class_method(mrb, klass, "now", timeNow, MRB_ARGS_NONE());
 	mrb_define_class_method(mrb, klass, "at", timeAt, MRB_ARGS_REQ(1));
diff --git a/binding-mruby/plane-binding.cpp b/binding-mruby/plane-binding.cpp
index ae8f439..1edc735 100644
--- a/binding-mruby/plane-binding.cpp
+++ b/binding-mruby/plane-binding.cpp
@@ -61,7 +61,7 @@ DEF_PROP_F(Plane, ZoomY)
 void
 planeBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "Plane", 0);
+	RClass *klass = defineClass(mrb, "Plane");
 
 	disposableBindingInit<Plane>     (mrb, klass);
 	viewportElementBindingInit<Plane>(mrb, klass);
diff --git a/binding-mruby/sprite-binding.cpp b/binding-mruby/sprite-binding.cpp
index 2eabc71..415bd5e 100644
--- a/binding-mruby/sprite-binding.cpp
+++ b/binding-mruby/sprite-binding.cpp
@@ -100,7 +100,7 @@ DEF_PROP_F(Sprite, WavePhase)
 void
 spriteBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "Sprite", 0);
+	RClass *klass = defineClass(mrb, "Sprite");
 
 	disposableBindingInit     <Sprite>(mrb, klass);
 	flashableBindingInit      <Sprite>(mrb, klass);
diff --git a/binding-mruby/table-binding.cpp b/binding-mruby/table-binding.cpp
index e81bd17..0ccc038 100644
--- a/binding-mruby/table-binding.cpp
+++ b/binding-mruby/table-binding.cpp
@@ -145,7 +145,7 @@ MARSH_LOAD_FUN(Table)
 void
 tableBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "Table", 0);
+	RClass *klass = defineClass(mrb, "Table");
 
 	mrb_define_class_method(mrb, klass, "_load", TableLoad, MRB_ARGS_REQ(1));
 	serializableBindingInit<Table>(mrb, klass);
diff --git a/binding-mruby/tilemap-binding.cpp b/binding-mruby/tilemap-binding.cpp
index a1d52dc..a117533 100644
--- a/binding-mruby/tilemap-binding.cpp
+++ b/binding-mruby/tilemap-binding.cpp
@@ -142,13 +142,13 @@ DEF_PROP_I(Tilemap, OY)
 void
 tilemapBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "TilemapAutotiles", 0);
+	RClass *klass = defineClass(mrb, "TilemapAutotiles");
 
 	mrb_define_method(mrb, klass, "[]=", tilemapAutotilesSet, MRB_ARGS_REQ(2));
 	mrb_define_method(mrb, klass, "[]", tilemapAutotilesGet, MRB_ARGS_REQ(1));
 	mrb_define_method(mrb, klass, "inspect", inspectObject, MRB_ARGS_NONE());
 
-	klass = mrb_define_class(mrb, "Tilemap", 0);
+	klass = defineClass(mrb, "Tilemap");
 
 	disposableBindingInit<Tilemap>(mrb, klass);
 
diff --git a/binding-mruby/viewport-binding.cpp b/binding-mruby/viewport-binding.cpp
index 0426fac..2a52884 100644
--- a/binding-mruby/viewport-binding.cpp
+++ b/binding-mruby/viewport-binding.cpp
@@ -81,7 +81,7 @@ DEF_PROP_I(Viewport, OY)
 void
 viewportBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "Viewport", 0);
+	RClass *klass = defineClass(mrb, "Viewport");
 
 	disposableBindingInit  <Viewport>(mrb, klass);
 	flashableBindingInit   <Viewport>(mrb, klass);
diff --git a/binding-mruby/window-binding.cpp b/binding-mruby/window-binding.cpp
index fe9afcf..9c2410a 100644
--- a/binding-mruby/window-binding.cpp
+++ b/binding-mruby/window-binding.cpp
@@ -73,7 +73,7 @@ DEF_PROP_I(Window, ContentsOpacity)
 void
 windowBindingInit(mrb_state *mrb)
 {
-	RClass *klass = mrb_define_class(mrb, "Window", 0);
+	RClass *klass = defineClass(mrb, "Window");
 
 	disposableBindingInit     <Window>(mrb, klass);
 	viewportElementBindingInit<Window>(mrb, klass);