diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index fbbccd8172f6..b388f7d8aefe 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -220,6 +220,17 @@ checkConfigError 'A definition for option .* is not of type .path in the Nix sto
 checkConfigError 'A definition for option .* is not of type .path in the Nix store.. Definition values:\n\s*- In .*: ".*/store/.links"' config.pathInStore.bad4 ./types.nix
 checkConfigError 'A definition for option .* is not of type .path in the Nix store.. Definition values:\n\s*- In .*: "/foo/bar"' config.pathInStore.bad5 ./types.nix
 
+# types.fileset
+checkConfigOutput '^0$' config.filesetCardinal.ok1 ./fileset.nix
+checkConfigOutput '^1$' config.filesetCardinal.ok2 ./fileset.nix
+checkConfigOutput '^1$' config.filesetCardinal.ok3 ./fileset.nix
+checkConfigOutput '^1$' config.filesetCardinal.ok4 ./fileset.nix
+checkConfigOutput '^0$' config.filesetCardinal.ok5 ./fileset.nix
+checkConfigError 'A definition for option .* is not of type .fileset.. Definition values:\n.*' config.filesetCardinal.err1 ./fileset.nix
+checkConfigError 'A definition for option .* is not of type .fileset.. Definition values:\n.*' config.filesetCardinal.err2 ./fileset.nix
+checkConfigError 'A definition for option .* is not of type .fileset.. Definition values:\n.*' config.filesetCardinal.err3 ./fileset.nix
+checkConfigError 'A definition for option .* is not of type .fileset.. Definition values:\n.*' config.filesetCardinal.err4 ./fileset.nix
+
 # Check boolean option.
 checkConfigOutput '^false$' config.enable ./declare-enable.nix
 checkConfigError 'The option .* does not exist. Definition values:\n\s*- In .*: true' config.enable ./define-enable.nix
diff --git a/lib/tests/modules/fileset.nix b/lib/tests/modules/fileset.nix
new file mode 100644
index 000000000000..40b1a8ef601f
--- /dev/null
+++ b/lib/tests/modules/fileset.nix
@@ -0,0 +1,50 @@
+{ config, lib, ... }:
+
+let
+  inherit (lib)
+    mkOption
+    mkIf
+    types
+    mapAttrs
+    length
+    ;
+  inherit (lib.fileset)
+    empty
+    unions
+    toList
+    ;
+in
+
+{
+  options = {
+    fileset = mkOption { type = with types; lazyAttrsOf fileset; };
+
+    ## The following option is only here as a proxy to test `fileset` that does
+    ## not work so well with `modules.sh` because it is not JSONable. It exposes
+    ## the number of elements in the fileset.
+    filesetCardinal = mkOption { default = mapAttrs (_: fs: length (toList fs)) config.fileset; };
+  };
+
+  config = {
+    fileset.ok1 = empty;
+    fileset.ok2 = ./fileset;
+    fileset.ok3 = unions [
+      empty
+      ./fileset
+    ];
+    # fileset.ok4: see imports below
+    fileset.ok5 = mkIf false ./fileset;
+
+    fileset.err1 = 1;
+    fileset.err2 = "foo";
+    fileset.err3 = "./.";
+    fileset.err4 = [ empty ];
+
+  };
+
+  imports = [
+    { fileset.ok4 = ./fileset; }
+    { fileset.ok4 = empty; }
+    { fileset.ok4 = ./fileset; }
+  ];
+}
diff --git a/lib/tests/modules/fileset/keepme b/lib/tests/modules/fileset/keepme
new file mode 100644
index 000000000000..27b2fabd2c27
--- /dev/null
+++ b/lib/tests/modules/fileset/keepme
@@ -0,0 +1 @@
+Do not remove. This file is used by the tests in `../fileset.nix`.