diff --git a/CMakeLists.txt b/CMakeLists.txt
index 527552896..37756dfb8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -212,9 +212,18 @@ option(FT_DISABLE_HARFBUZZ
 cmake_dependent_option(FT_DYNAMIC_HARFBUZZ
   "Load HarfBuzz library dynamically at runtime, if possible." ON
   "NOT FT_DISABLE_HARFBUZZ" OFF)
+cmake_dependent_option(FT_USE_HARFBUZZ_CALLBACKS
+  "Let HarfBuzz library inject callback methods at runtime." OFF
+  "NOT FT_DISABLE_HARFBUZZ;NOT FT_DYNAMIC_HARFBUZZ" OFF)
 cmake_dependent_option(FT_REQUIRE_HARFBUZZ
   "Require HarfBuzz for improving auto-hinting of OpenType fonts." OFF
   "NOT FT_DISABLE_HARFBUZZ" OFF)
+cmake_dependent_option(FT_USE_HARFBUZZ_CALLING_CONVENTION_CDECL
+  "use HarfBuzz library as cdecl." OFF
+  "NOT FT_DISABLE_HARFBUZZ" OFF)
+cmake_dependent_option(FT_USE_HARFBUZZ_CALLING_CONVENTION_STDCALL
+  "use HarfBuzz library as stdcall." OFF
+  "NOT FT_DISABLE_HARFBUZZ;NOT FT_USE_HARFBUZZ_CALLING_CONVENTION_CDECL" OFF)
 
 option(FT_DISABLE_BROTLI
   "Disable support of compressed WOFF2 fonts." OFF)
@@ -282,10 +291,13 @@ if (NOT FT_DISABLE_HARFBUZZ)
         endif()
       endif()
     endif()
+  elseif(FT_USE_HARFBUZZ_CALLBACKS)
+    set(FT_HARFBUZZ_CALLBACKS_ENABLED TRUE)
   endif()
-
   if (FT_DYNAMIC_HARFBUZZ_ENABLED)
     message(STATUS "Enabled dynamic loading of HarfBuzz library at runtime.")
+  elseif (FT_HARFBUZZ_CALLBACKS_ENABLED)
+    message(STATUS "Enable HarfBuzz to inject callbacks into FreeType.")
   elseif (FT_REQUIRE_HARFBUZZ)
     find_package(HarfBuzz ${HARFBUZZ_MIN_VERSION} REQUIRED)
   else ()
@@ -414,7 +426,7 @@ if (PNG_FOUND)
     "/\\* +(#define +FT_CONFIG_OPTION_USE_PNG) +\\*/" "\\1"
     FTOPTION_H "${FTOPTION_H}")
 endif ()
-if (HARFBUZZ_FOUND OR FT_DYNAMIC_HARFBUZZ_ENABLED)
+if (HARFBUZZ_FOUND OR FT_DYNAMIC_HARFBUZZ_ENABLED OR FT_HARFBUZZ_CALLBACKS_ENABLED)
   string(REGEX REPLACE
     "/\\* +(#define +FT_CONFIG_OPTION_USE_HARFBUZZ) +\\*/" "\\1"
     FTOPTION_H "${FTOPTION_H}")
@@ -422,7 +434,20 @@ if (HARFBUZZ_FOUND OR FT_DYNAMIC_HARFBUZZ_ENABLED)
     string(REGEX REPLACE
       "/\\* +(#define +FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC) +\\*/" "\\1"
       FTOPTION_H "${FTOPTION_H}")
+  elseif (FT_HARFBUZZ_CALLBACKS_ENABLED)
+    string(REGEX REPLACE
+      "/\\* +(#define +FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS) +\\*/" "\\1"
+      FTOPTION_H "${FTOPTION_H}")
   endif ()
+  if (FT_USE_HARFBUZZ_CALLING_CONVENTION_CDECL)
+    string(REGEX REPLACE
+      "/\\* +(#define +FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_CDECL) +\\*/" "\\1"
+      FTOPTION_H "${FTOPTION_H}")
+  elseif(FT_USE_HARFBUZZ_CALLING_CONVENTION_STDCALL)
+    string(REGEX REPLACE
+      "/\\* +(#define +FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_STDCALL) +\\*/" "\\1"
+      FTOPTION_H "${FTOPTION_H}")
+  endif()
 endif ()
 if (BROTLIDEC_FOUND)
   string(REGEX REPLACE
@@ -625,7 +650,7 @@ if (FT_DYNAMIC_HARFBUZZ_ENABLED AND FT_NEED_LIBDL)
   target_link_libraries(freetype PRIVATE dl)
   list(APPEND PKGCONFIG_LIBS_PRIVATE " -ldl")
 endif ()
-if (HarfBuzz_FOUND AND (NOT FT_DYNAMIC_HARFBUZZ_ENABLED))
+if (HarfBuzz_FOUND AND (NOT FT_DYNAMIC_HARFBUZZ_ENABLED) AND (NOT FT_HARFBUZZ_CALLBACKS_ENABLED))
   target_link_libraries(freetype PRIVATE HarfBuzz::HarfBuzz)
   list(APPEND PKGCONFIG_REQUIRES_PRIVATE "harfbuzz >= ${HARFBUZZ_MIN_VERSION}")
 endif ()
diff --git a/builds/unix/configure.raw b/builds/unix/configure.raw
index 62be4672a..37d665e1b 100644
--- a/builds/unix/configure.raw
+++ b/builds/unix/configure.raw
@@ -441,7 +441,7 @@ fi
 # check for system libharfbuzz
 
 AC_ARG_WITH([harfbuzz],
-  [AS_HELP_STRING([--with-harfbuzz=@<:@yes|dynamic|no|auto@:>@],
+  [AS_HELP_STRING([--with-harfbuzz=@<:@yes|dynamic|no|callbacks|auto@:>@],
                   [improve auto-hinting of OpenType fonts @<:@default=auto@:>@])],
   [], [with_harfbuzz=auto])
 
@@ -505,6 +505,14 @@ if test x"$have_harfbuzz" = xno; then
       ;;
     esac
   fi
+
+
+have_harfbuzz_callbacks=no
+if test x"$have_harfbuzz" = xno; then
+  if test x"$with_harfbuzz" = xcallbacks; then
+    have_harfbuzz_callbacks=yes
+    have_harfbuzz="yes (callbacks)"
+  fi
 fi
 
 if test x"$have_harfbuzz" = xno; then
@@ -1203,6 +1211,25 @@ if test "$have_harfbuzz_dynamic" != no; then
 else
   ftoption_unset FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC
 fi
+if test "$have_harfbuzz_callbacks" != no; then
+  ftoption_set FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS
+else
+  ftoption_unset FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS
+fi
+AC_ARG_WITH([harfbuzz-calling-convention],
+  [AS_HELP_STRING([--with-harfbuzz-calling-convention=@<:@auto|cdecl|stdcall@:>@],
+                  [calling convention of harfbuzz library @<:@default=auto@:>@])],
+  [], [with_harfbuzz_calling_convention=auto])
+if test x"$with_harfbuzz_calling_convention" = xcdecl; then
+  ftoption_set FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_CDECL
+else
+  ftoption_unset FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_CDECL
+fi
+if test x"$with_harfbuzz_calling_convention" = xstdcall; then
+  ftoption_set FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_STDCALL
+else
+  ftoption_unset FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_STDCALL
+fi
 if test "$have_brotli" != no; then
   CFLAGS="$CFLAGS $BROTLI_CFLAGS"
   LDFLAGS="$LDFLAGS $BROTLI_LIBS"
diff --git a/include/freetype/config/ftoption.h b/include/freetype/config/ftoption.h
index 073a507c0..b48277e32 100644
--- a/include/freetype/config/ftoption.h
+++ b/include/freetype/config/ftoption.h
@@ -317,6 +317,64 @@ FT_BEGIN_HEADER
    */
 /* #define FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
 
+  /**************************************************************************
+   *
+   * HarfBuzz callbacks support.
+   *
+   *   Define this macro if you want the HarfBuzz library to inject callback
+   *   functions to FreeType
+   *
+   *   This option has no effect if `FT_CONFIG_OPTION_USE_HARFBUZZ` is not
+   *   defined.
+   *
+   *   When this option is enabled, FreeType will not load or link to the 
+   *   HarfBuzz library. Instead, the HarfBuzz library is expected to set
+   *   use property 'harfbuzz-callbacks' to pass callback functions into 
+   *   FreeType.
+   *
+   *   If you use a build system like cmake or the `configure` script,
+   *   options set by those programs have precedence, overwriting the value
+   *   here with the configured one.
+   */
+/* #define FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS */
+
+  /**************************************************************************
+   *
+   * HarfBuzz dynamic/callbacks calling convention.
+   *
+   *   Define this macro if the HarfBuzz library is using cdecl calling
+   *   convention
+   *
+   *   This option has no effect if not using harfbuzz mode 'dynamic' or
+   *   'callbacks'.
+   *
+   *   When this option is enabled, FreeType will consider loaded or 
+   *   injected HarfBuzz-related functions as __cdecl.
+   *
+   *   If you use a build system like cmake or the `configure` script,
+   *   options set by those programs have precedence, overwriting the value
+   *   here with the configured one.
+   */
+/* #define FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_CDECL */
+
+  /**************************************************************************
+   *
+   * HarfBuzz dynamic/callbacks calling convention.
+   *
+   *   Define this macro if the HarfBuzz library is using stdcall calling
+   *   convention
+   *
+   *   This option has no effect if not using harfbuzz mode 'dynamic' or
+   *   'callbacks'.
+   *
+   *   When this option is enabled, FreeType will consider loaded or 
+   *   injected HarfBuzz-related functions as __stdcall.
+   *
+   *   If you use a build system like cmake or the `configure` script,
+   *   options set by those programs have precedence, overwriting the value
+   *   here with the configured one.
+   */
+/* #define FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_STDCALL */
 
   /**************************************************************************
    *
diff --git a/src/autofit/ft-hb-decls.h b/include/freetype/ft-hb-decls.h
similarity index 84%
rename from src/autofit/ft-hb-decls.h
rename to include/freetype/ft-hb-decls.h
index 032d4d37a..db6976dd4 100644
--- a/src/autofit/ft-hb-decls.h
+++ b/include/freetype/ft-hb-decls.h
@@ -27,90 +27,90 @@
 
   /* All HarfBuzz function declarations used by FreeType, taken    */
   /* from various public HarfBuzz header files.  The wrapper macro */
-  /* `HB_EXTERN` is defined in `ft-hb.h`.                          */
+  /* `FT_HB_EXTERN` is defined in `ft-hb.h`.                          */
 
 
 /* hb-blob.h */
 
-HB_EXTERN(hb_blob_t *,
+FT_HB_EXTERN(hb_blob_t *,
 hb_blob_create,(const char        *data,
 		unsigned int       length,
 		hb_memory_mode_t   mode,
 		void              *user_data,
 		hb_destroy_func_t  destroy))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_blob_destroy,(hb_blob_t *blob))
 
 
 /* hb-buffer.h */
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_buffer_add_utf8,(hb_buffer_t  *buffer,
 		    const char   *text,
 		    int           text_length,
 		    unsigned int  item_offset,
 		    int           item_length))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_buffer_clear_contents,(hb_buffer_t *buffer))
 
-HB_EXTERN(hb_buffer_t *,
+FT_HB_EXTERN(hb_buffer_t *,
 hb_buffer_create,(void))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_buffer_destroy,(hb_buffer_t *buffer))
 
-HB_EXTERN(hb_glyph_info_t *,
+FT_HB_EXTERN(hb_glyph_info_t *,
 hb_buffer_get_glyph_infos,(hb_buffer_t  *buffer,
 			   unsigned int *length))
 
-HB_EXTERN(hb_glyph_position_t *,
+FT_HB_EXTERN(hb_glyph_position_t *,
 hb_buffer_get_glyph_positions,(hb_buffer_t  *buffer,
 			       unsigned int *length))
 
-HB_EXTERN(unsigned int,
+FT_HB_EXTERN(unsigned int,
 hb_buffer_get_length,(const hb_buffer_t *buffer))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_buffer_guess_segment_properties,(hb_buffer_t *buffer))
 
 
 /* hb-face.h */
 
-HB_EXTERN(hb_face_t *,
+FT_HB_EXTERN(hb_face_t *,
 hb_face_create,(hb_blob_t    *blob,
 		unsigned int  index))
 
-HB_EXTERN(hb_face_t *,
+FT_HB_EXTERN(hb_face_t *,
 hb_face_create_for_tables,(hb_reference_table_func_t  reference_table_func,
 			   void                      *user_data,
 			   hb_destroy_func_t          destroy))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_face_destroy,(hb_face_t *face))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_face_set_index,(hb_face_t    *face,
 		   unsigned int  index))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_face_set_upem,(hb_face_t    *face,
 		  unsigned int  upem))
 
 
 /* hb-font.h */
 
-HB_EXTERN(hb_font_t *,
+FT_HB_EXTERN(hb_font_t *,
 hb_font_create,(hb_face_t *face))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_font_destroy,(hb_font_t *font))
 
-HB_EXTERN(hb_face_t *,
+FT_HB_EXTERN(hb_face_t *,
 hb_font_get_face,(hb_font_t *font))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_font_set_scale,(hb_font_t *font,
 		   int x_scale,
 		   int y_scale))
@@ -118,7 +118,7 @@ hb_font_set_scale,(hb_font_t *font,
 
 /* hb-ot-layout.h */
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_ot_layout_collect_lookups,(hb_face_t      *face,
 			      hb_tag_t        table_tag,
 			      const hb_tag_t *scripts,
@@ -126,7 +126,7 @@ hb_ot_layout_collect_lookups,(hb_face_t      *face,
 			      const hb_tag_t *features,
 			      hb_set_t       *lookup_indexes /* OUT */))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_ot_layout_lookup_collect_glyphs,(hb_face_t    *face,
 				    hb_tag_t      table_tag,
 				    unsigned int  lookup_index,
@@ -135,14 +135,14 @@ hb_ot_layout_lookup_collect_glyphs,(hb_face_t    *face,
 				    hb_set_t     *glyphs_after,  /* OUT.  May be NULL */
 				    hb_set_t     *glyphs_output  /* OUT.  May be NULL */))
 
-HB_EXTERN(hb_bool_t,
+FT_HB_EXTERN(hb_bool_t,
 hb_ot_layout_lookup_would_substitute,(hb_face_t            *face,
 				      unsigned int          lookup_index,
 				      const hb_codepoint_t *glyphs,
 				      unsigned int          glyphs_length,
 				      hb_bool_t             zero_context))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_ot_tags_from_script_and_language,(hb_script_t   script,
 				     hb_language_t language,
 				     unsigned int *script_count /* IN/OUT */,
@@ -153,48 +153,48 @@ hb_ot_tags_from_script_and_language,(hb_script_t   script,
 
 /* hb-set.h */
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_set_add,(hb_set_t       *set,
 	    hb_codepoint_t  codepoint))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_set_clear,(hb_set_t *set))
 
-HB_EXTERN(hb_set_t *,
+FT_HB_EXTERN(hb_set_t *,
 hb_set_create,(void))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_set_destroy,(hb_set_t *set))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_set_del,(hb_set_t       *set,
 	    hb_codepoint_t  codepoint))
 
-HB_EXTERN(hb_bool_t,
+FT_HB_EXTERN(hb_bool_t,
 hb_set_has,(const hb_set_t *set,
 	    hb_codepoint_t  codepoint))
 
-HB_EXTERN(hb_bool_t,
+FT_HB_EXTERN(hb_bool_t,
 hb_set_is_empty,(const hb_set_t *set))
 
-HB_EXTERN(hb_bool_t,
+FT_HB_EXTERN(hb_bool_t,
 hb_set_next,(const hb_set_t *set,
 	     hb_codepoint_t *codepoint))
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_set_subtract,(hb_set_t       *set,
 		 const hb_set_t *other))
 
 
 /* hb-shape.h */
 
-HB_EXTERN(void,
+FT_HB_EXTERN(void,
 hb_shape,(hb_font_t           *font,
 	  hb_buffer_t         *buffer,
 	  const hb_feature_t  *features,
 	  unsigned int         num_features))
 
-HB_EXTERN(hb_bool_t,
+FT_HB_EXTERN(hb_bool_t,
 hb_version_atleast,(unsigned int major,
 		    unsigned int minor,
 		    unsigned int micro))
diff --git a/include/freetype/ft-hb-functype.h b/include/freetype/ft-hb-functype.h
new file mode 100644
index 000000000..615461076
--- /dev/null
+++ b/include/freetype/ft-hb-functype.h
@@ -0,0 +1,70 @@
+/****************************************************************************
+ *
+ * ft-hb-functype.h
+ *
+ *   FreeType-HarfBuzz bridge (specification).
+ *
+ * Copyright (C) 2025 by
+ * 6ziv.
+ *
+ * This file is part of the FreeType project, and may only be used,
+ * modified, and distributed under the terms of the FreeType project
+ * license, LICENSE.TXT.  By continuing to use, modify, or distribute
+ * this file you indicate that you have read the license and
+ * understand and accept it fully.
+ *
+ *
+ * Originally located in src/autofit/ft-hb.h
+ * Move to a public header so that external projects can rely on this.
+ *
+ */
+
+#ifndef FT_HB_FUNCTYPE_H
+#define FT_HB_FUNCTYPE_H
+
+#include <freetype/ft-hb-types.h>
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )   || \
+    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
+
+#include <freetype/config/ftoption.h>
+
+#if defined(FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_CDECL)
+
+#if defined( __GNUC__ )
+#define FT_HB_CALLBACK
+#elif defined( _MSC_VER)
+#define FT_HB_CALLBACK __cdecl
+#endif
+
+#elif defined(FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_STDCALL) /* FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_CDECL */
+
+#if defined( __GNUC__ )
+#define FT_HB_CALLBACK __attribute__((stdcall))
+#elif defined( _MSC_VER)
+#define FT_HB_CALLBACK __stdcall
+#endif
+
+#endif /* FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_CDECL */
+
+#ifndef FT_HB_CALLBACK
+#define FT_HB_CALLBACK
+#endif
+
+#define FT_HB_EXTERN( ret, name, args ) \
+  typedef ret (FT_HB_CALLBACK *ft_ ## name ## _func_t) args;
+#include <freetype/ft-hb-decls.h>
+#undef FT_HB_EXTERN
+
+typedef struct ft_hb_funcs_t
+{
+
+    #define FT_HB_EXTERN( ret, name, args ) \
+  ft_ ## name ## _func_t  name;
+#include <freetype/ft-hb-decls.h>
+#undef FT_HB_EXTERN
+
+} ft_hb_funcs_t;
+
+#endif
+
+#endif /* FT_HB_FUNCTYPE_H */
\ No newline at end of file
diff --git a/src/autofit/ft-hb-types.h b/include/freetype/ft-hb-types.h
similarity index 100%
rename from src/autofit/ft-hb-types.h
rename to include/freetype/ft-hb-types.h
diff --git a/meson.build b/meson.build
index eec558373..d95b61505 100644
--- a/meson.build
+++ b/meson.build
@@ -183,6 +183,9 @@ ft2_public_headers = files([
   'include/freetype/ttnameid.h',
   'include/freetype/tttables.h',
   'include/freetype/tttags.h',
+  'include/freetype/ft-hb-types.h',
+  'include/freetype/ft-hb-decls.h',
+  'include/freetype/ft-hb-functype.h'
 ])
 
 ft2_config_headers = files([
@@ -388,10 +391,31 @@ if not harfbuzz_dep.found() and \
   endif
 endif
 
+if harfbuzz_opt == 'callbacks'
+  ftoption_command += [
+    '--enable=FT_CONFIG_OPTION_USE_HARFBUZZ',
+    '--enable=FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS',
+  ]
+endif
+
 if harfbuzz_opt == 'disabled' or harfbuzz_opt == 'auto'
   harfbuzz_opt = 'NO'
 endif
 
+if harfbuzz_opt == 'dynamic' or harfbuzz_opt == 'callbacks'
+  harfbuzz_calling_convention = get_option('harfbuzz_calling_convention')
+  if harfbuzz_calling_convention == 'cdecl'
+    ftoption_command += [
+      '--enable=FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_CDECL',
+    ]
+  endif
+  if harfbuzz_calling_convention == 'stdcall'
+    ftoption_command += [
+      '--enable=FT_CONFIG_OPTION_USE_HARFBUZZ_CALLING_CONVENTION_STDCALL',
+    ]
+  endif
+endif
+
 # Brotli decompression support.
 brotli_dep = dependency('libbrotlidec',
   required: get_option('brotli'))
diff --git a/meson_options.txt b/meson_options.txt
index 67d0fa313..fdb9bf41f 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -24,12 +24,21 @@ option('bzip2',
 
 option('harfbuzz',
   type: 'combo',
-  choices: ['auto', 'enabled', 'dynamic', 'disabled'],
+  choices: ['auto', 'enabled', 'dynamic', 'disabled', 'callbacks'],
   value: 'auto',
   description: 'Use Harfbuzz library to improve auto-hinting;'
                + ' if available, many glyphs not directly addressable'
                + ' by a font\'s character map will be hinted also')
 
+option('harfbuzz_calling_convention',
+  type: 'combo',
+  choices: ['auto', 'stdcall', 'cdecl'],
+  value: 'auto',
+  description: 'Calling-convention for HarfBuzz. Only used when using'
+               + ' harfbuzz=\'dynamic\' or harfbuzz=\'callbacks\'. If'
+               + ' unspecified or set to \'auto\', no specifier will'
+               + ' be added.')
+
 option('mmap',
   type: 'feature',
   value: 'auto',
diff --git a/src/autofit/afmodule.c b/src/autofit/afmodule.c
index 57d5d47df..b44681702 100644
--- a/src/autofit/afmodule.c
+++ b/src/autofit/afmodule.c
@@ -275,7 +275,16 @@
 
       return error;
     }
-
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )           && \
+    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
+#if defined ( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )
+#error "Can not set both dynamic harfbuzz and injected harfbuzz callbacks"
+#endif
+    else if ( !ft_strcmp( property_name, "harfbuzz-callbacks" ) )
+    {
+      module->hb_funcs = (ft_hb_funcs_t*)value;
+    }
+#endif
     FT_TRACE2(( "af_property_set: missing property `%s'\n",
                 property_name ));
     return FT_THROW( Missing_Property );
@@ -362,7 +371,17 @@
 
       return error;
     }
-
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )           && \
+    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
+#if defined ( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )
+#error "Can not set both dynamic harfbuzz and injected harfbuzz callbacks"
+#endif
+    else if ( !ft_strcmp( property_name, "harfbuzz-callbacks" ) )
+    {
+      ft_hb_funcs_t **val               = (ft_hb_funcs_t **)value;
+      *val = module->hb_funcs;
+    }
+#endif
     FT_TRACE2(( "af_property_get: missing property `%s'\n",
                 property_name ));
     return FT_THROW( Missing_Property );
diff --git a/src/autofit/afmodule.h b/src/autofit/afmodule.h
index 1f8a68122..695b4aa63 100644
--- a/src/autofit/afmodule.h
+++ b/src/autofit/afmodule.h
@@ -41,8 +41,9 @@ FT_BEGIN_HEADER
     FT_Bool       no_stem_darkening;
     FT_Int        darken_params[8];
 
-#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )         && \
-    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )               && \
+    ( defined( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )     || \
+      defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS ) )
     ft_hb_funcs_t*  hb_funcs;
 #endif
 
diff --git a/src/autofit/ft-hb.c b/src/autofit/ft-hb.c
index ed438da6a..889b749ee 100644
--- a/src/autofit/ft-hb.c
+++ b/src/autofit/ft-hb.c
@@ -131,14 +131,14 @@
       goto Fail;
 
     /* Load all symbols we use. */
-#define HB_EXTERN( ret, name, args )  \
+#define FT_HB_EXTERN( ret, name, args )  \
   {                                   \
     funcs->name = DLSYM( lib, name ); \
     if ( !funcs->name )               \
       goto Fail;                      \
   }
-#include "ft-hb-decls.h"
-#undef HB_EXTERN
+#include <freetype/internal/ft-hb-decls.h>
+#undef FT_HB_EXTERN
 
 #undef DLSYM
 
@@ -179,6 +179,14 @@
 
 #else /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
 
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )         && \
+    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
+  FT_LOCAL_DEF( FT_Bool )
+  ft_hb_enabled( struct AF_FaceGlobalsRec_  *globals )
+  {
+    return globals->module->hb_funcs != NULL;
+  }
+#else /* !FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS*/
   FT_LOCAL_DEF( FT_Bool )
   ft_hb_enabled( struct AF_FaceGlobalsRec_  *globals )
   {
@@ -191,6 +199,8 @@
 #endif
   }
 
+#endif /* !FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS */
+
 #endif /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
 
 
diff --git a/src/autofit/ft-hb.h b/src/autofit/ft-hb.h
index d2cc0482e..4b13aaab1 100644
--- a/src/autofit/ft-hb.h
+++ b/src/autofit/ft-hb.h
@@ -27,23 +27,13 @@ FT_BEGIN_HEADER
 
 #ifdef FT_CONFIG_OPTION_USE_HARFBUZZ
 
-#  include "ft-hb-types.h"
+#  include <freetype/ft-hb-functype.h>
+
+#  if defined( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )   || \
+      defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
 
 #  ifdef FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC
 
-#    define HB_EXTERN( ret, name, args ) \
-              typedef ret (*ft_ ## name ## _func_t) args;
-#    include "ft-hb-decls.h"
-#    undef HB_EXTERN
-
-  typedef struct ft_hb_funcs_t
-  {
-#    define HB_EXTERN( ret, name, args ) \
-              ft_ ## name ## _func_t  name;
-#    include "ft-hb-decls.h"
-#    undef HB_EXTERN
-  } ft_hb_funcs_t;
-
   struct  AF_ModuleRec_;
 
   FT_LOCAL( void )
@@ -52,14 +42,16 @@ FT_BEGIN_HEADER
   FT_LOCAL( void )
   ft_hb_funcs_done( struct AF_ModuleRec_  *af_module );
 
+#  endif /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
+
 #    define hb( x )  globals->module->hb_funcs->hb_ ## x
 
-#  else /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
+#  else /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC && !FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS*/
 
-#    define HB_EXTERN( ret, name, args ) \
+#    define FT_HB_EXTERN( ret, name, args ) \
               ret name args;
-#    include "ft-hb-decls.h"
-#    undef HB_EXTERN
+#    include <freetype/ft-hb-decls.h>
+#    undef FT_HB_EXTERN
 
 #    define hb( x )  hb_ ## x
 
diff --git a/src/autofit/rules.mk b/src/autofit/rules.mk
index 9e39db33c..45d9aae46 100644
--- a/src/autofit/rules.mk
+++ b/src/autofit/rules.mk
@@ -53,8 +53,7 @@ AUTOF_DRV_H := $(AUTOF_DRV_SRC:%c=%h)     \
                $(AUTOF_DIR)/afstyles.h    \
                $(AUTOF_DIR)/aftypes.h     \
                $(AUTOF_DIR)/afws-decl.h   \
-               $(AUTOF_DIR)/afws-iter.h   \
-               $(AUTOF_DIR)/ft-hb-decls.h
+               $(AUTOF_DIR)/afws-iter.h
 
 
 # AUTOF driver object(s)