diff --git a/src/hb-blob.cc b/src/hb-blob.cc
index 51f22ce4d..4b036e804 100644
--- a/src/hb-blob.cc
+++ b/src/hb-blob.cc
@@ -57,8 +57,6 @@ DEFINE_NULL_INSTANCE (hb_blob_t) =
 {
   HB_OBJECT_HEADER_STATIC,
 
-  true, /* immutable */
-
   nullptr, /* data */
   0, /* length */
   HB_MEMORY_MODE_READONLY, /* mode */
@@ -299,12 +297,10 @@ hb_blob_get_user_data (hb_blob_t          *blob,
 void
 hb_blob_make_immutable (hb_blob_t *blob)
 {
-  if (hb_object_is_inert (blob))
-    return;
-  if (blob->immutable)
+  if (hb_object_is_immutable (blob))
     return;
 
-  blob->immutable = true;
+  hb_object_make_immutable (blob);
 }
 
 /**
@@ -320,7 +316,7 @@ hb_blob_make_immutable (hb_blob_t *blob)
 hb_bool_t
 hb_blob_is_immutable (hb_blob_t *blob)
 {
-  return blob->immutable;
+  return hb_object_is_immutable (blob);
 }
 
 
@@ -454,7 +450,7 @@ hb_blob_t::try_make_writable_inplace (void)
 bool
 hb_blob_t::try_make_writable (void)
 {
-  if (this->immutable)
+  if (hb_object_is_immutable (this))
     return false;
 
   if (this->mode == HB_MEMORY_MODE_WRITABLE)
diff --git a/src/hb-blob.hh b/src/hb-blob.hh
index 0181e94a4..1f7499fbf 100644
--- a/src/hb-blob.hh
+++ b/src/hb-blob.hh
@@ -70,8 +70,6 @@ struct hb_blob_t
   public:
   hb_object_header_t header;
 
-  bool immutable;
-
   const char *data;
   unsigned int length;
   hb_memory_mode_t mode;
diff --git a/src/hb-face.cc b/src/hb-face.cc
index 7ca4b1ba2..50ab10e38 100644
--- a/src/hb-face.cc
+++ b/src/hb-face.cc
@@ -82,8 +82,6 @@ DEFINE_NULL_INSTANCE (hb_face_t) =
 {
   HB_OBJECT_HEADER_STATIC,
 
-  true, /* immutable */
-
   nullptr, /* reference_table_func */
   nullptr, /* user_data */
   nullptr, /* destroy */
@@ -336,12 +334,10 @@ hb_face_get_user_data (const hb_face_t    *face,
 void
 hb_face_make_immutable (hb_face_t *face)
 {
-  if (unlikely (hb_object_is_inert (face)))
-    return;
-  if (face->immutable)
+  if (hb_object_is_immutable (face))
     return;
 
-  face->immutable = true;
+  hb_object_make_immutable (face);
 }
 
 /**
@@ -357,7 +353,7 @@ hb_face_make_immutable (hb_face_t *face)
 hb_bool_t
 hb_face_is_immutable (const hb_face_t *face)
 {
-  return face->immutable;
+  return hb_object_is_immutable (face);
 }
 
 
@@ -408,7 +404,7 @@ void
 hb_face_set_index (hb_face_t    *face,
 		   unsigned int  index)
 {
-  if (face->immutable)
+  if (hb_object_is_immutable (face))
     return;
 
   face->index = index;
@@ -443,7 +439,7 @@ void
 hb_face_set_upem (hb_face_t    *face,
 		  unsigned int  upem)
 {
-  if (face->immutable)
+  if (hb_object_is_immutable (face))
     return;
 
   face->upem = upem;
@@ -478,7 +474,7 @@ void
 hb_face_set_glyph_count (hb_face_t    *face,
 			 unsigned int  glyph_count)
 {
-  if (face->immutable)
+  if (hb_object_is_immutable (face))
     return;
 
   face->num_glyphs = glyph_count;
diff --git a/src/hb-face.hh b/src/hb-face.hh
index 89673ff84..520bdfdf8 100644
--- a/src/hb-face.hh
+++ b/src/hb-face.hh
@@ -43,8 +43,6 @@ struct hb_face_t
 {
   hb_object_header_t header;
 
-  hb_bool_t immutable;
-
   hb_reference_table_func_t  reference_table_func;
   void                      *user_data;
   hb_destroy_func_t          destroy;
diff --git a/src/hb-font.cc b/src/hb-font.cc
index 86b03f4b6..567cdedc0 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -471,8 +471,6 @@ DEFINE_NULL_INSTANCE (hb_font_funcs_t) =
 {
   HB_OBJECT_HEADER_STATIC,
 
-  true, /* immutable */
-
   {
 #define HB_FONT_FUNC_IMPLEMENT(name) nullptr,
     HB_FONT_FUNCS_IMPLEMENT_CALLBACKS
@@ -495,8 +493,6 @@ DEFINE_NULL_INSTANCE (hb_font_funcs_t) =
 static const hb_font_funcs_t _hb_font_funcs_default = {
   HB_OBJECT_HEADER_STATIC,
 
-  true, /* immutable */
-
   {
 #define HB_FONT_FUNC_IMPLEMENT(name) nullptr,
     HB_FONT_FUNCS_IMPLEMENT_CALLBACKS
@@ -645,12 +641,10 @@ hb_font_funcs_get_user_data (hb_font_funcs_t    *ffuncs,
 void
 hb_font_funcs_make_immutable (hb_font_funcs_t *ffuncs)
 {
-  if (unlikely (hb_object_is_inert (ffuncs)))
-    return;
-  if (ffuncs->immutable)
+  if (hb_object_is_immutable (ffuncs))
     return;
 
-  ffuncs->immutable = true;
+  hb_object_make_immutable (ffuncs);
 }
 
 /**
@@ -666,7 +660,7 @@ hb_font_funcs_make_immutable (hb_font_funcs_t *ffuncs)
 hb_bool_t
 hb_font_funcs_is_immutable (hb_font_funcs_t *ffuncs)
 {
-  return ffuncs->immutable;
+  return hb_object_is_immutable (ffuncs);
 }
 
 
@@ -678,7 +672,7 @@ hb_font_funcs_set_##name##_func (hb_font_funcs_t             *ffuncs,    \
                                  void                        *user_data, \
                                  hb_destroy_func_t            destroy)   \
 {                                                                        \
-  if (ffuncs->immutable) {                                               \
+  if (hb_object_is_immutable (ffuncs)) {                                 \
     if (destroy)                                                         \
       destroy (user_data);                                               \
     return;                                                              \
@@ -1299,8 +1293,6 @@ DEFINE_NULL_INSTANCE (hb_font_t) =
 {
   HB_OBJECT_HEADER_STATIC,
 
-  true, /* immutable */
-
   nullptr, /* parent */
   const_cast<hb_face_t *> (&_hb_Null_hb_face_t),
 
@@ -1525,15 +1517,13 @@ hb_font_get_user_data (hb_font_t          *font,
 void
 hb_font_make_immutable (hb_font_t *font)
 {
-  if (unlikely (hb_object_is_inert (font)))
-    return;
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   if (font->parent)
     hb_font_make_immutable (font->parent);
 
-  font->immutable = true;
+  hb_object_make_immutable (font);
 }
 
 /**
@@ -1549,7 +1539,7 @@ hb_font_make_immutable (hb_font_t *font)
 hb_bool_t
 hb_font_is_immutable (hb_font_t *font)
 {
-  return font->immutable;
+  return hb_object_is_immutable (font);
 }
 
 /**
@@ -1565,7 +1555,7 @@ void
 hb_font_set_parent (hb_font_t *font,
 		    hb_font_t *parent)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   if (!parent)
@@ -1607,7 +1597,7 @@ void
 hb_font_set_face (hb_font_t *font,
 		  hb_face_t *face)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   if (unlikely (!face))
@@ -1654,7 +1644,8 @@ hb_font_set_funcs (hb_font_t         *font,
 		   void              *font_data,
 		   hb_destroy_func_t  destroy)
 {
-  if (font->immutable) {
+  if (hb_object_is_immutable (font))
+  {
     if (destroy)
       destroy (font_data);
     return;
@@ -1689,7 +1680,8 @@ hb_font_set_funcs_data (hb_font_t         *font,
 		        hb_destroy_func_t  destroy)
 {
   /* Destroy user_data? */
-  if (font->immutable) {
+  if (hb_object_is_immutable (font))
+  {
     if (destroy)
       destroy (font_data);
     return;
@@ -1718,7 +1710,7 @@ hb_font_set_scale (hb_font_t *font,
 		   int x_scale,
 		   int y_scale)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   font->x_scale = x_scale;
@@ -1759,7 +1751,7 @@ hb_font_set_ppem (hb_font_t *font,
 		  unsigned int x_ppem,
 		  unsigned int y_ppem)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   font->x_ppem = x_ppem;
@@ -1799,7 +1791,7 @@ hb_font_get_ppem (hb_font_t *font,
 void
 hb_font_set_ptem (hb_font_t *font, float ptem)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   font->ptem = ptem;
@@ -1846,7 +1838,7 @@ hb_font_set_variations (hb_font_t *font,
 			const hb_variation_t *variations,
 			unsigned int variations_length)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   if (!variations_length)
@@ -1877,7 +1869,7 @@ hb_font_set_var_coords_design (hb_font_t *font,
 			       const float *coords,
 			       unsigned int coords_length)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   int *normalized = coords_length ? (int *) calloc (coords_length, sizeof (int)) : nullptr;
@@ -1898,7 +1890,7 @@ hb_font_set_var_coords_normalized (hb_font_t *font,
 				   const int *coords, /* 2.14 normalized */
 				   unsigned int coords_length)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   int *copy = coords_length ? (int *) calloc (coords_length, sizeof (coords[0])) : nullptr;
diff --git a/src/hb-font.hh b/src/hb-font.hh
index 3dce233db..fb29bcc22 100644
--- a/src/hb-font.hh
+++ b/src/hb-font.hh
@@ -63,8 +63,6 @@ struct hb_font_funcs_t
 {
   hb_object_header_t header;
 
-  hb_bool_t immutable;
-
   struct {
 #define HB_FONT_FUNC_IMPLEMENT(name) void *name;
     HB_FONT_FUNCS_IMPLEMENT_CALLBACKS
@@ -102,8 +100,6 @@ struct hb_font_t
 {
   hb_object_header_t header;
 
-  hb_bool_t immutable;
-
   hb_font_t *parent;
   hb_face_t *face;
 
diff --git a/src/hb-ft.cc b/src/hb-ft.cc
index 5e0511052..8b80b960b 100644
--- a/src/hb-ft.cc
+++ b/src/hb-ft.cc
@@ -135,7 +135,7 @@ _hb_ft_font_destroy (void *data)
 void
 hb_ft_font_set_load_flags (hb_font_t *font, int load_flags)
 {
-  if (font->immutable)
+  if (hb_object_is_immutable (font))
     return;
 
   if (font->destroy != (hb_destroy_func_t) _hb_ft_font_destroy)
diff --git a/src/hb-object.hh b/src/hb-object.hh
index 309aa2b41..74340c555 100644
--- a/src/hb-object.hh
+++ b/src/hb-object.hh
@@ -197,7 +197,12 @@ struct hb_object_header_t
   hb_atomic_int_t writable;
   hb_atomic_ptr_t<hb_user_data_array_t> user_data;
 };
-#define HB_OBJECT_HEADER_STATIC {HB_REFERENCE_COUNT_INIT, HB_ATOMIC_INT_INIT (0), HB_ATOMIC_PTR_INIT (nullptr)}
+#define HB_OBJECT_HEADER_STATIC \
+	{ \
+	  HB_REFERENCE_COUNT_INIT, \
+	  HB_ATOMIC_INT_INIT (false), \
+	  HB_ATOMIC_PTR_INIT (nullptr) \
+	}
 
 
 /*
@@ -248,9 +253,9 @@ static inline bool hb_object_is_immutable (const Type *obj)
   return !obj->header.writable.get_relaxed ();
 }
 template <typename Type>
-static inline bool hb_object_make_immutable (const Type *obj)
+static inline void hb_object_make_immutable (const Type *obj)
 {
-  return !obj->header.writable.set_relaxed (false);
+  obj->header.writable.set_relaxed (false);
 }
 template <typename Type>
 static inline Type *hb_object_reference (Type *obj)
diff --git a/src/hb-unicode.cc b/src/hb-unicode.cc
index 8cf7898a1..5accf3643 100644
--- a/src/hb-unicode.cc
+++ b/src/hb-unicode.cc
@@ -187,7 +187,6 @@ DEFINE_NULL_INSTANCE (hb_unicode_funcs_t) =
   HB_OBJECT_HEADER_STATIC,
 
   nullptr, /* parent */
-  true, /* immutable */
   {
 #define HB_UNICODE_FUNC_IMPLEMENT(name) hb_unicode_##name##_nil,
     HB_UNICODE_FUNCS_IMPLEMENT_CALLBACKS
@@ -303,12 +302,10 @@ hb_unicode_funcs_get_user_data (hb_unicode_funcs_t *ufuncs,
 void
 hb_unicode_funcs_make_immutable (hb_unicode_funcs_t *ufuncs)
 {
-  if (unlikely (hb_object_is_inert (ufuncs)))
-    return;
-  if (ufuncs->immutable)
+  if (hb_object_is_immutable (ufuncs))
     return;
 
-  ufuncs->immutable = true;
+  hb_object_make_immutable (ufuncs);
 }
 
 /**
@@ -324,7 +321,7 @@ hb_unicode_funcs_make_immutable (hb_unicode_funcs_t *ufuncs)
 hb_bool_t
 hb_unicode_funcs_is_immutable (hb_unicode_funcs_t *ufuncs)
 {
-  return ufuncs->immutable;
+  return hb_object_is_immutable (ufuncs);
 }
 
 /**
@@ -352,7 +349,7 @@ hb_unicode_funcs_set_##name##_func (hb_unicode_funcs_t		   *ufuncs,	\
 				    void			   *user_data,	\
 				    hb_destroy_func_t		    destroy)	\
 {										\
-  if (ufuncs->immutable)							\
+  if (hb_object_is_immutable (ufuncs))						\
     return;									\
 										\
   if (ufuncs->destroy.name)							\
diff --git a/src/hb-unicode.hh b/src/hb-unicode.hh
index 0b66ce8a1..d3fd5ea4b 100644
--- a/src/hb-unicode.hh
+++ b/src/hb-unicode.hh
@@ -66,8 +66,6 @@ struct hb_unicode_funcs_t
 
   hb_unicode_funcs_t *parent;
 
-  bool immutable;
-
 #define HB_UNICODE_FUNC_IMPLEMENT(return_type, name) \
   inline return_type name (hb_codepoint_t unicode) { return func.name (this, unicode, user_data.name); }
 HB_UNICODE_FUNCS_IMPLEMENT_CALLBACKS_SIMPLE