diff --git a/lib/types.nix b/lib/types.nix
index dd1e8ab9d0165..4ddd36c97520e 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -475,9 +475,10 @@ rec {
       check = isString;
       merge = loc: defs: concatStringsSep sep (getValues defs);
       functor = (defaultFunctor name) // {
-        payload = sep;
-        binOp = sepLhs: sepRhs:
-          if sepLhs == sepRhs then sepLhs
+        payload = { inherit sep; };
+        type = payload: types.separatedString payload.sep;
+        binOp = lhs: rhs:
+          if lhs.sep == rhs.sep then { inherit (lhs) sep; }
           else null;
       };
     };
@@ -1014,7 +1015,11 @@ rec {
           else "conjunction";
         check = flip elem values;
         merge = mergeEqualOption;
-        functor = (defaultFunctor name) // { payload = values; binOp = a: b: unique (a ++ b); };
+        functor = (defaultFunctor name) // {
+          payload = { inherit values; };
+          type = payload: types.enum payload.values;
+          binOp = a: b: { values = unique (a.values ++ b.values); };
+        };
       };
 
     # Either value of type `t1` or `t2`.
diff --git a/nixos/doc/manual/redirects.json b/nixos/doc/manual/redirects.json
index 5f7bf93db21ed..6f897ce7a9917 100644
--- a/nixos/doc/manual/redirects.json
+++ b/nixos/doc/manual/redirects.json
@@ -1844,6 +1844,12 @@
   "sec-release-25.05-notable-changes": [
     "release-notes.html#sec-release-25.05-notable-changes"
   ],
+  "sec-release-25.05-lib": [
+    "release-notes.html#sec-release-25.05-lib"
+  ],
+  "sec-release-25.05-lib-breaking": [
+    "release-notes.html#sec-release-25.05-lib-breaking"
+  ],
   "sec-release-24.11": [
     "release-notes.html#sec-release-24.11"
   ],
diff --git a/nixos/doc/manual/release-notes/rl-2505.section.md b/nixos/doc/manual/release-notes/rl-2505.section.md
index f173d0d93b1d3..f3a58367e055f 100644
--- a/nixos/doc/manual/release-notes/rl-2505.section.md
+++ b/nixos/doc/manual/release-notes/rl-2505.section.md
@@ -118,3 +118,11 @@
 - `bind.cacheNetworks` now only controls access for recursive queries, where it previously controlled access for all queries.
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
+
+## Nixpkgs Library {#sec-release-25.05-lib}
+
+### Breaking changes {#sec-release-25.05-lib-breaking}
+
+- Structure of the `functor` of some types has changed. `functor` is an implementation detail and should not be relied upon. If you did rely on it let us know in this [PR](https://github.com/NixOS/nixpkgs/pull/363565).
+  - [`lib.types.enum`](https://nixos.org/manual/nixos/unstable/#sec-option-types-basic): Previously the `functor.payload` was the list of enum values directly. Now it is an attribute set containing the values in the `values` attribute.
+  - [`lib.types.separatedString`](https://nixos.org/manual/nixos/unstable/#sec-option-types-string): Previously the `functor.payload` was the seperator directly. Now it is an attribute set containing the seperator in the `sep` attribute.