diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index c4e9f4ede..169f451c6 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -9,7 +9,7 @@ jobs:
   build:
     strategy:
       matrix:
-        version: [4.08.1, 5.0.0]
+        version: [5.0.0]
         os: [ubuntu-latest, macOS-latest]
 
     runs-on: ${{ matrix.os }}
diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index c3275f1de..8d6ef3512 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -10,7 +10,7 @@ jobs:
     # GitHub allows matrix variables in more places than env variables
     strategy:
       matrix:
-        version: [4.08.1]
+        version: [5.0.0]
         os: [ubuntu-latest]
 
     runs-on: ${{ matrix.os }}
diff --git a/sail_json_backend.opam b/sail_json_backend.opam
new file mode 100644
index 000000000..b4f01652e
--- /dev/null
+++ b/sail_json_backend.opam
@@ -0,0 +1,43 @@
+# This file is generated by dune, edit dune-project instead
+opam-version: "2.0"
+version: "0.17"
+synopsis: "Sail to JSON formatting"
+maintainer: ["Sail Devs <cl-sail-dev@lists.cam.ac.uk>"]
+authors: [
+  "Alasdair Armstrong"
+  "Thomas Bauereiss"
+  "Brian Campbell"
+  "Shaked Flur"
+  "Jonathan French"
+  "Kathy Gray"
+  "Robert Norton"
+  "Christopher Pulte"
+  "Peter Sewell"
+  "Mark Wassell"
+]
+license: "BSD-2-Clause"
+homepage: "https://github.com/rems-project/sail"
+bug-reports: "https://github.com/rems-project/sail/issues"
+depends: [
+  "dune" {>= "3.0"}
+  "libsail" {= version}
+  "omd" {>= "1.3.1" & < "1.4.0"}
+  "odoc" {with-doc}
+]
+build: [
+  ["dune" "subst"] {dev}
+  [
+    "dune"
+    "build"
+    "-p"
+    name
+    "-j"
+    jobs
+    "--promote-install-files=false"
+    "@install"
+    "@runtest" {with-test}
+    "@doc" {with-doc}
+  ]
+  ["dune" "install" "-p" name "--create-install-files" name]
+]
+dev-repo: "git+https://github.com/rems-project/sail.git"