diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e4656fafb..41e2e521d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -49,7 +49,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: Set up OCaml ${{ matrix.ocaml-compiler }}
-        uses: avsm/setup-ocaml@v2
+        uses: avsm/setup-ocaml@v3
         with:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
           dune-cache: true
diff --git a/src/ml_gdkpixbuf.c b/src/ml_gdkpixbuf.c
index 51ff28502..64855aa52 100644
--- a/src/ml_gdkpixbuf.c
+++ b/src/ml_gdkpixbuf.c
@@ -59,7 +59,7 @@ CAMLprim value ml_gdk_pixbuf_set_marshal_use_rle (value v)
   return Val_unit;
 }
 
-static void ml_GdkPixbuf_serialize (value v, unsigned long *wsize_32, unsigned long *wsize_64)
+static void ml_GdkPixbuf_serialize (value v, uintnat *wsize_32, uintnat *wsize_64)
 {
   GdkPixbuf *pb = GdkPixbuf_val(v);
   GdkPixdata pixdata;
@@ -75,7 +75,7 @@ static void ml_GdkPixbuf_serialize (value v, unsigned long *wsize_32, unsigned l
   *wsize_64 = 8;
 }
 
-static unsigned long ml_GdkPixbuf_deserialize (void *dst)
+static uintnat ml_GdkPixbuf_deserialize (void *dst)
 {
   GError *error = NULL;
   GdkPixdata pixdata;