diff --git a/src/hb-font.cc b/src/hb-font.cc
index e257cd87d4480b088845b4a286777dfaa1f4e67a..fd5df93ff501706c1598036f1420a66a20347d51 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -141,6 +141,12 @@ hb_font_funcs_make_immutable (hb_font_funcs_t *ffuncs)
   ffuncs->immutable = TRUE;
 }
 
+hb_bool_t
+hb_font_funcs_is_immutable (hb_font_funcs_t *ffuncs)
+{
+  return ffuncs->immutable = TRUE;
+}
+
 
 void
 hb_font_funcs_set_glyph_func (hb_font_funcs_t *ffuncs,
diff --git a/src/hb-font.h b/src/hb-font.h
index a7b6d8f6c21f403ffc0ee360b4b0ddc0aa27316b..266b74a8366332272fd0472999dd7ab9dba4403c 100644
--- a/src/hb-font.h
+++ b/src/hb-font.h
@@ -91,6 +91,8 @@ hb_font_funcs_copy (hb_font_funcs_t *ffuncs);
 void
 hb_font_funcs_make_immutable (hb_font_funcs_t *ffuncs);
 
+hb_bool_t
+hb_font_funcs_is_immutable (hb_font_funcs_t *ffuncs);
 
 /* funcs */
 
diff --git a/src/hb-unicode.c b/src/hb-unicode.c
index 19a891b4a84bd3c06377b4c29f29ea4ab968107e..280c61f9e1673d5fe06fcdc0679d769e64fe50cd 100644
--- a/src/hb-unicode.c
+++ b/src/hb-unicode.c
@@ -108,6 +108,12 @@ hb_unicode_funcs_make_immutable (hb_unicode_funcs_t *ufuncs)
   ufuncs->immutable = TRUE;
 }
 
+hb_bool_t
+hb_unicode_funcs_is_immutable (hb_unicode_funcs_t *ufuncs)
+{
+  return ufuncs->immutable;
+}
+
 
 void
 hb_unicode_funcs_set_mirroring_func (hb_unicode_funcs_t *ufuncs,
diff --git a/src/hb-unicode.h b/src/hb-unicode.h
index a84a948901089923807abc939cc373cf726ddddb..4edab48ae56152d44e13b1006c6f639d0cf22fc8 100644
--- a/src/hb-unicode.h
+++ b/src/hb-unicode.h
@@ -201,6 +201,8 @@ hb_unicode_funcs_copy (hb_unicode_funcs_t *ufuncs);
 void
 hb_unicode_funcs_make_immutable (hb_unicode_funcs_t *ufuncs);
 
+hb_bool_t
+hb_unicode_funcs_is_immutable (hb_unicode_funcs_t *ufuncs);
 
 /*
  * funcs