diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e24f79cb..43223eca 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,9 +10,11 @@ jobs:
     strategy:
       matrix:
         os:
-          - ubuntu-latest
+          # Error: Package 'darcs' has no installation candidate
+          # - ubuntu-latest
+          - ubuntu-22.04
           - macos-latest
-          # The CI does not support OCaml version 5.1 yet (at the time of writing).
+          # Native support for OCaml not verified yet.
           # - windows-latest
           # Either the waiting queue for FreeBSD is very long, or it is not available.
           # - freebsd-latest
diff --git a/.github/workflows/gh-pages.yml b/.github/workflows/gh-pages.yml
index 729734fe..a5fe7e39 100644
--- a/.github/workflows/gh-pages.yml
+++ b/.github/workflows/gh-pages.yml
@@ -16,7 +16,9 @@ jobs:
         uses: actions/cache@v2
         with:
           path: ~/.opam
-          key: opam-ubuntu-latest-5.2.0
+          # Error: Package 'darcs' has no installation candidate
+          # key: opam-ubuntu-latest-5.2.0
+          key: opam-ubuntu-22.04-5.2.0
 
       # - uses: actions/checkout@v2
       - uses: ocaml/setup-ocaml@v2
diff --git a/arrayjit/lib/ops.ml b/arrayjit/lib/ops.ml
index 15eeea5f..dc224567 100644
--- a/arrayjit/lib/ops.ml
+++ b/arrayjit/lib/ops.ml
@@ -238,10 +238,10 @@ let sexp_of_voidptr p = Sexp.Atom Ctypes.(string_of (ptr void) p)
 let compare_voidptr = Ctypes.ptr_compare
 let equal_voidptr : voidptr -> voidptr -> bool = phys_equal
 
-let c_rawptr_to_string (type elem) (ptr : nativeint) prec =
+let c_rawptr_to_string (ptr : nativeint) prec =
   "(" ^ c_typ_of_prec prec ^ "*)" ^ Nativeint.Hex.to_string ptr
 
-let rawptr_to_string_hum (type elem) (ptr : nativeint) prec =
+let rawptr_to_string_hum (ptr : nativeint) prec =
   "(" ^ hum_typ_of_prec prec ^ "*)" ^ Nativeint.Hex.to_string ptr
 
 let c_ptr_to_string (type elem) (ptr : elem Ctypes.ptr) prec =