diff --git a/flake.nix b/flake.nix
index e547846f8..f991e4d46 100644
--- a/flake.nix
+++ b/flake.nix
@@ -421,31 +421,26 @@
         dockerImage = lib.genAttrs linux64BitSystems (system: self.packages.${system}.dockerImage);
 
         # API docs for Nix's unstable internal C++ interfaces.
-        internal-api-docs =
-          with nixpkgsFor.x86_64-linux.native;
-          with commonDeps { inherit pkgs; };
+        internal-api-docs = let
+          nixpkgs = nixpkgsFor.x86_64-linux.native;
+          inherit (nixpkgs) pkgs;
+          comDeps = commonDeps { inherit pkgs; };
 
-          stdenv.mkDerivation {
-            pname = "nix-internal-api-docs";
-            inherit version;
-
-            src = nixSrc;
-
-            configureFlags = testConfigureFlags ++ internalApiDocsConfigureFlags;
-
-            nativeBuildInputs = nativeBuildDeps;
-            buildInputs = buildDeps ++ propagatedDeps
-              ++ awsDeps ++ checkDeps ++ internalApiDocsDeps;
-
-            dontBuild = true;
-
-            installTargets = [ "internal-api-html" ];
-
-            postInstall = ''
-              mkdir -p $out/nix-support
-              echo "doc internal-api-docs $out/share/doc/nix/internal-api/html" >> $out/nix-support/hydra-build-products
-            '';
+          nix = nixpkgs.pkgs.callPackage ./package.nix {
+            inherit versionSuffix fileset officialRelease buildUnreleasedNotes;
+            inherit (comDeps) changelog-d;
+            internalApiDocs = true;
+            boehmgc = comDeps.boehmgc-nix;
+            busybox-sandbox-shell = comDeps.sh;
           };
+        in
+          nix.overrideAttrs (prev: {
+            # This Hydra job is just for the internal API docs.
+            # We don't need the build artifacts here.
+            dontBuild = true;
+            doCheck = false;
+            doInstallCheck = false;
+          });
 
         # System tests.
         tests = import ./tests/nixos { inherit lib nixpkgs nixpkgsFor; } // {
diff --git a/package.nix b/package.nix
index a6933b0ab..73e887d8d 100644
--- a/package.nix
+++ b/package.nix
@@ -13,6 +13,7 @@
   brotli,
   bzip2,
   curl,
+  doxygen,
   editline,
   fileset,
   flex,
@@ -42,6 +43,7 @@
   officialRelease ? true,
   # Set to true to build the release notes for the next release.
   buildUnreleasedNotes ? false,
+  internalApiDocs ? false,
 
   # Not a real argument, just the only way to approximate let-binding some
   # stuff for argument defaults.
@@ -62,6 +64,13 @@
     "RAPIDCHECK_HEADERS=${lib.getDev rapidcheck}/extras/gtest/include"
   ];
 
+  # The internal API docs need these for the build, but if we're not building
+  # Nix itself, then these don't need to be propagated.
+  maybePropagatedInputs = [
+    boehmgc
+    nlohmann_json
+  ];
+
   # .gitignore has already been processed, so any changes in it are irrelevant
   # at this point. It is not represented verbatim for test purposes because
   # that would interfere with repo semantics.
@@ -98,7 +107,7 @@ in stdenv.mkDerivation (finalAttrs: {
       topLevelBuildFiles
       functionalTestFiles
       ./unit-test-data
-    ] ++ lib.optionals (!finalAttrs.dontBuild) [
+    ] ++ lib.optionals (!finalAttrs.dontBuild || internalApiDocs) [
       ./boehmgc-coroutine-sp-fallback.diff
       ./doc
       ./misc
@@ -132,7 +141,9 @@ in stdenv.mkDerivation (finalAttrs: {
     mercurial
     jq
   ] ++ lib.optional stdenv.hostPlatform.isLinux util-linuxMinimal
-    ++ lib.optional (!officialRelease && buildUnreleasedNotes) changelog-d;
+    ++ lib.optional (!officialRelease && buildUnreleasedNotes) changelog-d
+    ++ lib.optional internalApiDocs doxygen
+  ;
 
   buildInputs = [
     curl
@@ -153,6 +164,7 @@ in stdenv.mkDerivation (finalAttrs: {
     ++ lib.optional (stdenv.hostPlatform == stdenv.buildPlatform) aws-sdk-cpp-nix
     # FIXME(Qyriad): This is how the flake.nix version does it, but this is cursed.
     ++ lib.optionals (finalAttrs.doCheck) finalAttrs.passthru._checkInputs
+    ++ lib.optionals (finalAttrs.dontBuild) maybePropagatedInputs
   ;
 
   passthru._checkInputs = [
@@ -163,10 +175,7 @@ in stdenv.mkDerivation (finalAttrs: {
   # FIXME(Qyriad): remove at the end of refactoring.
   checkInputs = finalAttrs.passthru._checkInputs;
 
-  propagatedBuildInputs = [
-    boehmgc
-    nlohmann_json
-  ];
+  propagatedBuildInputs = lib.optionals (!finalAttrs.dontBuild) maybePropagatedInputs;
 
   disallowedReferences = [
     boost
@@ -198,10 +207,13 @@ in stdenv.mkDerivation (finalAttrs: {
   ] ++ [ "--sysconfdir=/etc" ]
     ++ lib.optional stdenv.hostPlatform.isStatic "--enable-embedded-sandbox-shell"
     ++ [ (lib.enableFeature finalAttrs.doCheck "tests") ]
-    ++ lib.optionals finalAttrs.doCheck testConfigureFlags
+    ++ lib.optionals (finalAttrs.doCheck || internalApiDocs) testConfigureFlags
     ++ lib.optional (!canRunInstalled) "--disable-doc-gen"
+    ++ [ (lib.enableFeature internalApiDocs "internal-api-docs") ]
   ;
 
+  installTargets = lib.optional internalApiDocs "internal-api-html";
+
   enableParallelBuilding = true;
 
   makeFlags = "profiledir=$(out)/etc/profile.d PRECOMPILE_HEADERS=1";
@@ -210,19 +222,20 @@ in stdenv.mkDerivation (finalAttrs: {
 
   installFlags = "sysconfdir=$(out)/etc";
 
-  postInstall = ''
-      mkdir -p $doc/nix-support
-      echo "doc manual $doc/share/doc/nix/manual" >> $doc/nix-support/hydra-build-products
-      ${lib.optionalString stdenv.hostPlatform.isStatic ''
-      mkdir -p $out/nix-support
-      echo "file binary-dist $out/bin/nix" >> $out/nix-support/hydra-build-products
-      ''}
-      ${lib.optionalString stdenv.isDarwin ''
-      install_name_tool \
-        -change ${boost}/lib/libboost_context.dylib \
-        $out/lib/libboost_context.dylib \
-        $out/lib/libnixutil.dylib
-      ''}
+  postInstall = lib.optionalString (!finalAttrs.dontBuild) ''
+    mkdir -p $doc/nix-support
+    echo "doc manual $doc/share/doc/nix/manual" >> $doc/nix-support/hydra-build-products
+  '' + lib.optionalString stdenv.hostPlatform.isStatic ''
+    mkdir -p $out/nix-support
+    echo "file binary-dist $out/bin/nix" >> $out/nix-support/hydra-build-products
+  '' + lib.optionalString stdenv.isDarwin ''
+    install_name_tool \
+      -change ${boost}/lib/libboost_context.dylib \
+      $out/lib/libboost_context.dylib \
+      $out/lib/libnixutil.dylib
+  '' + lib.optionalString internalApiDocs ''
+    mkdir -p $out/nix-support
+    echo "doc internal-api-docs $out/share/doc/nix/internal-api/html" >> "$out/nix-support/hydra-build-products"
   '';
 
   doInstallCheck = finalAttrs.doCheck;