diff --git a/tests/main.nix b/tests/main.nix
index 8f2aec013a..3fe4fcb262 100644
--- a/tests/main.nix
+++ b/tests/main.nix
@@ -6,7 +6,6 @@
   lib ? pkgs.lib,
   linkFarm,
   pkgs,
-  pkgsUnfree,
   self,
   system,
 }:
@@ -29,8 +28,10 @@ let
           inherit self system;
           inherit (self) inputs;
         };
+        nixpkgs.config = {
+          allowUnfree = true;
+        };
       };
-      pkgs = pkgsUnfree;
     };
 
   # List of files containing configurations
diff --git a/tests/test-sources/modules/nixpkgs.nix b/tests/test-sources/modules/nixpkgs.nix
index 6efce76a93..54efc9977b 100644
--- a/tests/test-sources/modules/nixpkgs.nix
+++ b/tests/test-sources/modules/nixpkgs.nix
@@ -71,4 +71,25 @@
         }
       ];
     };
+
+  # Test that a nixpkgs revision can be specified using `nixpkgs.source`
+  source =
+    { pkgs, ... }:
+    {
+      test.runNvim = false;
+
+      nixpkgs.source = builtins.fetchTarball {
+        url = "https://github.com/NixOS/nixpkgs/archive/1807c2b91223227ad5599d7067a61665c52d1295.tar.gz";
+        sha256 = "0xnj86751780hg1zhx9rjkbjr0sx0wps4wxz7zryvrj6hgwrng1z";
+      };
+
+      assertions = [
+        {
+          assertion = pkgs.lib.version == "24.11pre-git";
+          message = ''
+            Expected `pkgs.lib.version` to be "24.11pre-git", but found "${pkgs.lib.version}"
+          '';
+        }
+      ];
+    };
 }