diff --git a/src/hb-font.cc b/src/hb-font.cc
index 15b7e6add..f1649ecd3 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -1624,6 +1624,7 @@ DEFINE_NULL_INSTANCE (hb_font_t) =
   HB_OBJECT_HEADER_STATIC,
 
   0, /* serial */
+  0, /* serial_coords */
 
   nullptr, /* parent */
   const_cast<hb_face_t *> (&_hb_Null_hb_face_t),
@@ -1929,7 +1930,7 @@ hb_font_is_immutable (hb_font_t *font)
  *
  * Since: REPLACEME.
  **/
-unsigned long
+unsigned int
 hb_font_get_serial (hb_font_t *font)
 {
   return font->serial;
@@ -2343,7 +2344,7 @@ hb_font_set_variations (hb_font_t            *font,
   if (hb_object_is_immutable (font))
     return;
 
-  font->serial++;
+  font->serial_coords = ++font->serial;
 
   if (!variations_length)
   {
@@ -2404,7 +2405,7 @@ hb_font_set_var_coords_design (hb_font_t    *font,
   if (hb_object_is_immutable (font))
     return;
 
-  font->serial++;
+  font->serial_coords = ++font->serial;
 
   int *normalized = coords_length ? (int *) hb_calloc (coords_length, sizeof (int)) : nullptr;
   float *design_coords = coords_length ? (float *) hb_calloc (coords_length, sizeof (float)) : nullptr;
@@ -2439,7 +2440,7 @@ hb_font_set_var_named_instance (hb_font_t *font,
   if (hb_object_is_immutable (font))
     return;
 
-  font->serial++;
+  font->serial_coords = ++font->serial;
 
   unsigned int coords_length = hb_ot_var_named_instance_get_design_coords (font->face, instance_index, nullptr, nullptr);
 
@@ -2477,7 +2478,7 @@ hb_font_set_var_coords_normalized (hb_font_t    *font,
   if (hb_object_is_immutable (font))
     return;
 
-  font->serial++;
+  font->serial_coords = ++font->serial;
 
   int *copy = coords_length ? (int *) hb_calloc (coords_length, sizeof (coords[0])) : nullptr;
   int *unmapped = coords_length ? (int *) hb_calloc (coords_length, sizeof (coords[0])) : nullptr;
diff --git a/src/hb-font.h b/src/hb-font.h
index 9eedf6469..ca6ecf796 100644
--- a/src/hb-font.h
+++ b/src/hb-font.h
@@ -1002,7 +1002,7 @@ hb_font_make_immutable (hb_font_t *font);
 HB_EXTERN hb_bool_t
 hb_font_is_immutable (hb_font_t *font);
 
-HB_EXTERN unsigned long
+HB_EXTERN unsigned int
 hb_font_get_serial (hb_font_t *font);
 
 HB_EXTERN void
diff --git a/src/hb-font.hh b/src/hb-font.hh
index 91dd0c968..952beabe1 100644
--- a/src/hb-font.hh
+++ b/src/hb-font.hh
@@ -104,7 +104,8 @@ DECLARE_NULL_INSTANCE (hb_font_funcs_t);
 struct hb_font_t
 {
   hb_object_header_t header;
-  unsigned long serial;
+  unsigned int serial;
+  unsigned int serial_coords;
 
   hb_font_t *parent;
   hb_face_t *face;