diff --git a/lib/modules.nix b/lib/modules.nix
index 61964d46678116e..dd58de08255ff90 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -744,6 +744,9 @@ let
           t' = opt.options.type;
           mergedType = t.typeMerge t'.functor;
           typesMergeable = mergedType != null;
+          applySet = if (bothHave "apply")
+                        then { apply = value: opt.options.apply (res.apply value); }
+                        else {};
           typeSet = if (bothHave "type") && typesMergeable
                        then { type = mergedType; }
                        else {};
@@ -752,7 +755,6 @@ let
       if bothHave "default" ||
          bothHave "example" ||
          bothHave "description" ||
-         bothHave "apply" ||
          (bothHave "type" && (! typesMergeable))
       then
         throw "The option `${showOption loc}' in `${opt._file}' is already declared in ${showFiles res.declarations}."
@@ -772,7 +774,7 @@ let
                 then [opt.pos]
                 else [{ file = opt._file; line = null; column = null; }]);
             options = submodules;
-          } // typeSet
+          } // applySet // typeSet
     ) { inherit loc; declarations = []; declarationPositions = []; options = []; } opts;
 
   /* Merge all the definitions of an option to produce the final
diff --git a/nixos/doc/manual/release-notes/rl-2405.section.md b/nixos/doc/manual/release-notes/rl-2405.section.md
index 858f1d2a61382b8..9637c80f652e47e 100644
--- a/nixos/doc/manual/release-notes/rl-2405.section.md
+++ b/nixos/doc/manual/release-notes/rl-2405.section.md
@@ -407,6 +407,8 @@ The pre-existing [services.ankisyncd](#opt-services.ankisyncd.enable) has been m
 
 - A stdenv's default set of hardening flags can now be set via its `bintools-wrapper`'s `defaultHardeningFlags` argument. A convenient stdenv adapter, `withDefaultHardeningFlags`, can be used to override an existing stdenv's `defaultHardeningFlags`.
 
+- The `apply` function passed to `mkOption` is now mergeable. This allows for accessing the previous value of the option, similar to the `prev`/`super` argument in `overlays`, `override` and `overrideAttrs`.
+
 - `libass` now uses the native CoreText backend on Darwin, which may fix subtitle rendering issues with `mpv`, `ffmpeg`, etc.
 
 - [Lilypond](https://lilypond.org/index.html) and [Denemo](https://www.denemo.org) are now compiled with Guile 3.0.