diff --git a/src/hb-blob-private.hh b/src/hb-blob-private.hh
new file mode 100644
index 000000000..0d567c288
--- /dev/null
+++ b/src/hb-blob-private.hh
@@ -0,0 +1,77 @@
+/*
+ * Copyright © 2009  Red Hat, Inc.
+ * Copyright © 2018  Google, Inc.
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Red Hat Author(s): Behdad Esfahbod
+ * Google Author(s): Behdad Esfahbod
+ */
+
+#ifndef HB_BLOB_PRIVATE_HH
+#define HB_BLOB_PRIVATE_HH
+
+#include "hb-private.hh"
+
+#include "hb-object-private.hh"
+
+
+/*
+ * hb_blob_t
+ */
+
+struct hb_blob_t
+{
+  inline void fini_shallow (void)
+  {
+    destroy_user_data ();
+  }
+
+  inline void destroy_user_data (void)
+  {
+    if (destroy)
+    {
+      destroy (user_data);
+      user_data = nullptr;
+      destroy = nullptr;
+    }
+  }
+
+  HB_INTERNAL bool try_make_writable (void);
+  HB_INTERNAL bool try_make_writable_inplace (void);
+  HB_INTERNAL bool try_make_writable_inplace_unix (void);
+
+  public:
+  hb_object_header_t header;
+  ASSERT_POD ();
+
+  bool immutable;
+
+  const char *data;
+  unsigned int length;
+  hb_memory_mode_t mode;
+
+  void *user_data;
+  hb_destroy_func_t destroy;
+};
+
+
+#endif /* HB_BLOB_PRIVATE_HH */