diff --git a/src/hb-draw.cc b/src/hb-draw.cc
index 46797e64e..14c73eafa 100644
--- a/src/hb-draw.cc
+++ b/src/hb-draw.cc
@@ -80,6 +80,56 @@ hb_draw_close_path_nil (hb_draw_funcs_t *dfuncs HB_UNUSED, void *draw_data HB_UN
 			void *user_data HB_UNUSED) {}
 
 
+static bool
+_hb_draw_funcs_set_preamble (hb_draw_funcs_t    *dfuncs,
+			     bool                func_is_null,
+			     void              **user_data,
+			     hb_destroy_func_t  *destroy)
+{
+  if (hb_object_is_immutable (dfuncs))
+  {
+    if (*destroy)
+      (*destroy) (*user_data);
+    return false;
+  }
+
+  if (func_is_null)
+  {
+    if (*destroy)
+      (*destroy) (*user_data);
+    *destroy = nullptr;
+    *user_data = nullptr;
+  }
+
+  return true;
+}
+
+static bool
+_hb_draw_funcs_set_middle (hb_draw_funcs_t   *dfuncs,
+			   void              *user_data,
+			   hb_destroy_func_t  destroy)
+{
+  if (user_data && !dfuncs->user_data)
+  {
+    dfuncs->user_data = (decltype (dfuncs->user_data)) hb_calloc (1, sizeof (*dfuncs->user_data));
+    if (unlikely (!dfuncs->user_data))
+      goto fail;
+  }
+  if (destroy && !dfuncs->destroy)
+  {
+    dfuncs->destroy = (decltype (dfuncs->destroy)) hb_calloc (1, sizeof (*dfuncs->destroy));
+    if (unlikely (!dfuncs->destroy))
+      goto fail;
+  }
+
+  return true;
+
+fail:
+  if (destroy)
+    (destroy) (user_data);
+  return false;
+}
+
 #define HB_DRAW_FUNC_IMPLEMENT(name)						\
 										\
 void										\
@@ -88,24 +138,14 @@ hb_draw_funcs_set_##name##_func (hb_draw_funcs_t	 *dfuncs,		\
 				 void			 *user_data,		\
 				 hb_destroy_func_t	  destroy)		\
 {										\
-  if (hb_object_is_immutable (dfuncs))						\
-    return;									\
+  if (!_hb_draw_funcs_set_preamble (dfuncs, !func, &user_data, &destroy))\
+      return;                                                            \
 										\
   if (dfuncs->destroy && dfuncs->destroy->name)					\
     dfuncs->destroy->name (!dfuncs->user_data ? nullptr : dfuncs->user_data->name); \
 									 \
-  if (user_data && !dfuncs->user_data)                                   \
-  {                                                                      \
-    dfuncs->user_data = (decltype (dfuncs->user_data)) hb_calloc (1, sizeof (*dfuncs->user_data)); \
-    if (unlikely (!dfuncs->user_data))                                   \
-      goto fail;                                                         \
-  }                                                                      \
-  if (destroy && !dfuncs->destroy)                                       \
-  {                                                                      \
-    dfuncs->destroy = (decltype (dfuncs->destroy)) hb_calloc (1, sizeof (*dfuncs->destroy)); \
-    if (unlikely (!dfuncs->destroy))                                     \
-      goto fail;                                                         \
-  }                                                                      \
+  if (!_hb_draw_funcs_set_middle (dfuncs, user_data, destroy))           \
+      return;                                                            \
 									\
   if (func) {								\
     dfuncs->func.name = func;						\
@@ -121,10 +161,6 @@ hb_draw_funcs_set_##name##_func (hb_draw_funcs_t	 *dfuncs,		\
       dfuncs->destroy->name = nullptr;					\
   }									\
   return;                                                                \
-                                                                         \
-fail:                                                                    \
-  if (destroy)                                                           \
-    destroy (user_data);                                                 \
 }
 
 HB_DRAW_FUNCS_IMPLEMENT_CALLBACKS
diff --git a/src/hb-font.cc b/src/hb-font.cc
index b3ac63aff..04dd30e29 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -823,10 +823,10 @@ hb_font_funcs_is_immutable (hb_font_funcs_t *ffuncs)
 
 
 static bool
-set_func_preamble (hb_font_funcs_t *ffuncs,
-		   bool func_is_null,
-		   void **user_data,
-		   hb_destroy_func_t *destroy)
+_hb_font_funcs_set_preamble (hb_font_funcs_t    *ffuncs,
+			     bool                func_is_null,
+			     void              **user_data,
+			     hb_destroy_func_t  *destroy)
 {
   if (hb_object_is_immutable (ffuncs))
   {
@@ -847,9 +847,9 @@ set_func_preamble (hb_font_funcs_t *ffuncs,
 }
 
 static bool
-set_func_middle (hb_font_funcs_t *ffuncs,
-		   void *user_data,
-		   hb_destroy_func_t destroy)
+_hb_font_funcs_set_middle (hb_font_funcs_t   *ffuncs,
+			   void              *user_data,
+			   hb_destroy_func_t  destroy)
 {
   if (user_data && !ffuncs->user_data)
   {
@@ -880,13 +880,13 @@ hb_font_funcs_set_##name##_func (hb_font_funcs_t             *ffuncs,    \
 				 void                        *user_data, \
 				 hb_destroy_func_t            destroy)   \
 {                                                                        \
-  if (!set_func_preamble (ffuncs, !func, &user_data, &destroy))          \
+  if (!_hb_font_funcs_set_preamble (ffuncs, !func, &user_data, &destroy))\
       return;                                                            \
 									 \
   if (ffuncs->destroy && ffuncs->destroy->name)                          \
     ffuncs->destroy->name (!ffuncs->user_data ? nullptr : ffuncs->user_data->name); \
                                                                          \
-  if (!set_func_middle (ffuncs, user_data, destroy))                     \
+  if (!_hb_font_funcs_set_middle (ffuncs, user_data, destroy))           \
       return;                                                            \
 									 \
   if (func) {                                                            \