Try #1025:

Author: iohk-bors[bot]

ci.nix

@@ -11,6 +11,7 @@
   nixpkgsVersions = {
     "R2003" = "nixpkgs-2003";
     "R2009" = "nixpkgs-2009";
+    "unstable" = "nixpkgs-unstable";
   };
   compilerNixNames = nixpkgsName: nixpkgs: builtins.mapAttrs (compiler-nix-name: runTests: {
     inherit (import ./default.nix { inherit checkMaterialization; }) nixpkgsArgs;
@@ -30,6 +31,9 @@
       ghc8102 = false;
       ghc8103 = true;
       ghc810220201118 = false;
+    } // nixpkgs.lib.optionalAttrs (nixpkgsName == "unstable") {
+      ghc884 = true;
+      ghc8103 = true;
     });
   systems = nixpkgs: nixpkgs.lib.filterAttrs (_: v: builtins.elem v supportedSystems) {
     # I wanted to take these from 'lib.systems.examples', but apparently there isn't one for linux!

nix/sources.json

@@ -116,5 +116,17 @@
         "type": "tarball",
         "url": "https://github.com/NixOS/nixpkgs/archive/f02bf8ffb9a5ec5e8f6f66f1e5544fd2aa1a0693.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs-unstable": {
+        "branch": "nixpkgs-unstable",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "1b77b735ea70c3dfbdab3eaa79aee48d75d3e162",
+        "sha256": "1i3whn84c4w7rhlgl9m8226qlgs7p86j7wpm4dgvv9mhzqph92zc",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/1b77b735ea70c3dfbdab3eaa79aee48d75d3e162.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }