diff --git a/.envrc b/.envrc
index cc94b51..517837c 100644
--- a/.envrc
+++ b/.envrc
@@ -1,2 +1,2 @@
-nix_direnv_watch_file *.cabal
+nix_direnv_watch_file *.cabal nix/*.nix
 use flake
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 170985a..0b93a1e 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -16,10 +16,10 @@ jobs:
       - uses: DeterminateSystems/nix-installer-action@main
         with:
           extra-conf: |
-            trusted-public-keys = cache.garnix.io:CTFPyKSLcx5RMJKfLo5EEPUObbA78b0YQ2DTCJXqr9g= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
-            substituters = https://cache.garnix.io?priority=41 https://cache.nixos.org/
+            trusted-public-keys = horizon.cachix.org-1:MeEEDRhRZTgv/FFGCv3479/dmJDfJ82G6kfUDxMSAw0= cache.garnix.io:CTFPyKSLcx5RMJKfLo5EEPUObbA78b0YQ2DTCJXqr9g= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+            substituters = https://horizon.cachix.org https://cache.garnix.io?priority=41 https://cache.nixos.org/
       - uses: DeterminateSystems/magic-nix-cache-action@main
       - uses: yaxitech/nix-install-pkgs-action@v3
         with:
           packages: "github:srid/nixci"
-      - run: nixci
+      - run: nixci -- --accept-flake-config
diff --git a/flake.nix b/flake.nix
index 3d87919..cc9b15f 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,7 +1,15 @@
 {
   description = "srid/haskell-template: Nix template for Haskell projects";
+
+  nixConfig = {
+    extra-substituters = "https://horizon.cachix.org";
+    extra-trusted-public-keys = "horizon.cachix.org-1:MeEEDRhRZTgv/FFGCv3479/dmJDfJ82G6kfUDxMSAw0=";
+  };
+
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    horizon-devtools.url = "git+https://gitlab.horizon-haskell.net/package-sets/horizon-devtools?ref=lts/ghc-9.6.x";
+    horizon-platform.url = "git+https://gitlab.horizon-haskell.net/package-sets/horizon-platform?ref=lts/ghc-9.6.x";
     systems.url = "github:nix-systems/default";
     flake-parts.url = "github:hercules-ci/flake-parts";
     haskell-flake.url = "github:srid/haskell-flake";
@@ -17,12 +25,18 @@
         inputs.haskell-flake.flakeModule
         inputs.treefmt-nix.flakeModule
         inputs.fourmolu-nix.flakeModule
+        (import ./nix/horizon-package-set.nix { inherit inputs; })
       ];
+      flake.flakeModules.horizon-package-set =
+        import ./nix/horizon-package-set.nix { inherit inputs; };
       perSystem = { self', system, lib, config, pkgs, ... }: {
         # Our only Haskell project. You can have multiple projects, but this template
         # has only one.
         # See https://github.com/srid/haskell-flake/blob/master/example/flake.nix
         haskellProjects.default = {
+          imports = [
+            inputs.self.haskellFlakeProjectModules.horizon-package-set
+          ];
           # To avoid unnecessary rebuilds, we filter projectRoot:
           # https://community.flake.parts/haskell-flake/local#rebuild
           projectRoot = builtins.toString (lib.fileset.toSource {
diff --git a/haskell-template.cabal b/haskell-template.cabal
index 8da86b6..7447d79 100644
--- a/haskell-template.cabal
+++ b/haskell-template.cabal
@@ -77,7 +77,7 @@ common shared
   build-depends:
     , aeson
     , async
-    , base          >=4.13.0.0 && <4.18.0.0.0
+    , base          >=4.13.0.0 && <5
     , data-default
     , directory
     , filepath
diff --git a/nix/horizon-package-set.nix b/nix/horizon-package-set.nix
new file mode 100644
index 0000000..6956715
--- /dev/null
+++ b/nix/horizon-package-set.nix
@@ -0,0 +1,14 @@
+# Use horizon package set for haskell-flake
+{ inputs, ... }:
+{
+  flake.haskellFlakeProjectModules.horizon-package-set = { pkgs, ... }: {
+    basePackages = inputs.horizon-platform.legacyPackages.${pkgs.system};
+
+    # Horizon maintains separate package set for devtools.
+    defaults.devShell.tools = _:
+      let devtools = inputs.horizon-devtools.legacyPackages.${pkgs.system};
+      in {
+        inherit (devtools) cabal-install ghcid haskell-language-server;
+      };
+  };
+}