diff --git a/lib/modules.nix b/lib/modules.nix
index 17bc1f1d766479c..f7711261998a2e6 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -807,6 +807,9 @@ let
 
     in warnDeprecation opt //
       { value = builtins.addErrorContext "while evaluating the option `${showOption loc}':" value;
+        # The merged value before applying the options `apply` function to it.
+        # In general though, `apply` should not be used, it's an anti-pattern.
+        beforeApply = res.mergedValue;
         inherit (res.defsFinal') highestPrio;
         definitions = map (def: def.value) res.defsFinal;
         files = map (def: def.file) res.defsFinal;
diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index 750b1d025e02614..a571f6a963624a3 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -69,6 +69,8 @@ checkConfigOutput '^"one two"$' config.result ./shorthand-meta.nix
 
 checkConfigOutput '^true$' config.result ./test-mergeAttrDefinitionsWithPrio.nix
 
+checkConfigOutput '^true$' config.okChecks ./before-apply.nix
+
 # Check that a module argument is passed, also when a default is available
 # (but not needed)
 #
diff --git a/lib/tests/modules/before-apply.nix b/lib/tests/modules/before-apply.nix
new file mode 100644
index 000000000000000..cb0f917e5e77755
--- /dev/null
+++ b/lib/tests/modules/before-apply.nix
@@ -0,0 +1,24 @@
+{ options, lib, ... }:
+
+# Tests wheter a apply function properly generates the `beforeApply` option attribute
+
+{
+  options = {
+    optionWithoutApply = lib.mkOption {
+      default = false;
+      type = lib.types.bool;
+    };
+
+    optionWithApply = lib.mkOption {
+      default = false;
+      type = lib.types.bool;
+      apply = x: !x;
+    };
+
+    okChecks = lib.mkOption {};
+  };
+  config.okChecks = builtins.addErrorContext "while evaluating the assertions" (
+    assert options.optionWithoutApply.beforeApply == options.optionWithoutApply.value;
+    assert options.optionWithApply.beforeApply == !options.optionWithApply.value;
+  true);
+}