diff --git a/doc/manual/default.nix b/doc/manual/default.nix
index 2225b515..5a0072a9 100644
--- a/doc/manual/default.nix
+++ b/doc/manual/default.nix
@@ -13,28 +13,30 @@ with pkgs;
 let
   lib = pkgs.lib;
 
+  gitHubDeclaration = user: repo: ref: subpath:
+    # Default to `master` if we don't know what revision the system
+    # configuration is using (custom nixpkgs, etc.).
+    let urlRef = if ref != null then ref else "master";
+    in {
+      url = "https://github.com/${user}/${repo}/blob/${urlRef}/${subpath}";
+      name = "<${repo}/${subpath}>";
+    };
+
   optionsDoc = buildPackages.nixosOptionsDoc {
-    inherit options revision;
+    inherit options;
     transformOptions = opt: opt // {
       # Clean up declaration sites to not refer to the nix-darwin source tree.
       # TODO: handle `extraSources`? (it's not set anywhere)
       declarations = map
         (decl:
           if lib.hasPrefix (toString prefix) (toString decl) then
-            let
-              subpath = lib.removePrefix "/"
-                (lib.removePrefix (toString prefix) (toString decl));
-            in {
-              url = "https://github.com/LnL7/nix-darwin/blob/${revision}/${subpath}";
-              name = "<nix-darwin/${subpath}>";
-            }
+            gitHubDeclaration "LnL7" "nix-darwin" revision
+              (lib.removePrefix "/"
+                (lib.removePrefix (toString prefix) (toString decl)))
           # TODO: handle this in a better way (may require upstream
           # changes to nixpkgs)
           else if decl == "lib/modules.nix" then
-            {
-              url = "https://github.com/NixOS/nixpkgs/blob/${nixpkgsRevision}/${decl}";
-              name = "<nixpkgs/${decl}>";
-            }
+            gitHubDeclaration "NixOS" "nixpkgs" nixpkgsRevision decl
           else decl)
         opt.declarations;
     };
@@ -73,7 +75,7 @@ in rec {
       cp -r ${pkgs.documentation-highlighter} $dst/highlightjs
 
       substitute ${./manual.md} manual.md \
-        --replace '@DARWIN_VERSION@' "${version}"\
+        --replace '@DARWIN_VERSION@' "${version}" \
         --replace \
           '@DARWIN_OPTIONS_JSON@' \
           ${optionsJSON}/share/doc/darwin/options.json
@@ -82,7 +84,7 @@ in rec {
       nixos-render-docs -j $NIX_BUILD_CORES manual html \
         --manpage-urls ${pkgs.writeText "manpage-urls.json" "{}"} \
         --revision ${lib.escapeShellArg revision} \
-        --generator "nixos-render-docs ${pkgs.lib.version}" \
+        --generator "nixos-render-docs ${lib.version}" \
         --stylesheet style.css \
         --stylesheet overrides.css \
         --stylesheet highlightjs/mono-blue.css \
diff --git a/modules/documentation/default.nix b/modules/documentation/default.nix
index 25165c94..2f3bb9a4 100644
--- a/modules/documentation/default.nix
+++ b/modules/documentation/default.nix
@@ -1,4 +1,4 @@
-toplevel@{ config, lib, pkgs, baseModules, modules, ... }:
+{ config, lib, pkgs, baseModules, modules, ... }:
 
 with lib;
 
@@ -25,15 +25,7 @@ let
     inherit pkgs config;
     version = config.system.darwinVersion;
     revision = config.system.darwinRevision;
-    nixpkgsRevision =
-      if toplevel.options.system.nixpkgsRevision.isDefined
-        then config.system.nixpkgsRevision
-
-        # If user does not use flakes and does not add rev to nixpkgs, we don't
-        # know which revision or even branch they're on. In this case we still want
-        # to link somewhere, so we hope that master hasn't changed too much.
-        else "master";
-
+    inherit (config.system) nixpkgsRevision;
     options =
       let
         scrubbedEval = evalModules {
diff --git a/modules/system/version.nix b/modules/system/version.nix
index 68019188..0824829c 100644
--- a/modules/system/version.nix
+++ b/modules/system/version.nix
@@ -67,8 +67,8 @@ in
 
     system.darwinRevision = mkOption {
       internal = true;
-      type = types.str;
-      default = "master";
+      type = types.nullOr types.str;
+      default = null;
       description = lib.mdDoc "The darwin git revision from which this configuration was built.";
     };
 
@@ -92,7 +92,8 @@ in
 
     system.nixpkgsRevision = mkOption {
       internal = true;
-      type = types.str;
+      type = types.nullOr types.str;
+      default = null;
       description = lib.mdDoc "The nixpkgs git revision from which this configuration was built.";
     };
   };