diff --git a/.github/workflows/guard_build_files.yml b/.github/workflows/guard_build_files.yml
new file mode 100644
index 0000000000..2f04b59e8f
--- /dev/null
+++ b/.github/workflows/guard_build_files.yml
@@ -0,0 +1,27 @@
+name: Guardian
+on:
+  pull_request:
+    branches:
+      - master
+      - stable
+jobs:
+  check_if_up-to-date:
+    name: Check if `build-files.txt` is up-to-date.
+    strategy:
+      fail-fast: true
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v7
+    - name: Created updated `build-files.txt`
+      run: |
+        find source -name '*.d' \
+          | \
+            LANG="" \
+            LC_ALL="" \
+            LC_CTYPE="" \
+            sort > build-files.txt.expected
+    - name: Show difference(s)
+      run: diff -u build-files.txt build-files.txt.expected
+    - name: Test whether `build-files.txt` is up-to-date
+      run: cmp build-files.txt build-files.txt.expected
diff --git a/build-files.txt b/build-files.txt
index 79b38b3b33..615bc33f9b 100644
--- a/build-files.txt
+++ b/build-files.txt
@@ -13,15 +13,20 @@ source/dub/description.d
 source/dub/dub.d
 source/dub/generators/build.d
 source/dub/generators/cmake.d
-source/dub/generators/ninja.d
 source/dub/generators/generator.d
+source/dub/generators/ninja.d
 source/dub/generators/sublimetext.d
 source/dub/generators/targetdescription.d
 source/dub/generators/visuald.d
 source/dub/init.d
+source/dub/internal/colorize/colors.d
+source/dub/internal/colorize/cwrite.d
+source/dub/internal/colorize/package.d
+source/dub/internal/colorize/winterm.d
 source/dub/internal/configy/attributes.d
 source/dub/internal/configy/backend/node.d
 source/dub/internal/configy/backend/yaml.d
+source/dub/internal/configy/dub_test.d
 source/dub/internal/configy/easy.d
 source/dub/internal/configy/exceptions.d
 source/dub/internal/configy/fieldref.d
@@ -52,8 +57,10 @@ source/dub/internal/dyaml/tagdirective.d
 source/dub/internal/dyaml/token.d
 source/dub/internal/git.d
 source/dub/internal/io/filesystem.d
+source/dub/internal/io/mockfs.d
 source/dub/internal/io/realfs.d
 source/dub/internal/libInputVisitor.d
+source/dub/internal/logging.d
 source/dub/internal/sdlang/ast.d
 source/dub/internal/sdlang/exception.d
 source/dub/internal/sdlang/lexer.d
@@ -62,22 +69,21 @@ source/dub/internal/sdlang/parser.d
 source/dub/internal/sdlang/symbol.d
 source/dub/internal/sdlang/token.d
 source/dub/internal/sdlang/util.d
+source/dub/internal/temp_files.d
 source/dub/internal/tinyendian.d
 source/dub/internal/undead/xml.d
-source/dub/internal/temp_files.d
 source/dub/internal/utils.d
 source/dub/internal/vibecompat/core/file.d
+source/dub/internal/vibecompat/data/conv.d
 source/dub/internal/vibecompat/data/json.d
 source/dub/internal/vibecompat/data/serialization.d
+source/dub/internal/vibecompat/data/traits.d
+source/dub/internal/vibecompat/data/typetuple.d
+source/dub/internal/vibecompat/data/uda.d
 source/dub/internal/vibecompat/inet/path.d
 source/dub/internal/vibecompat/inet/path2.d
 source/dub/internal/vibecompat/inet/url.d
 source/dub/internal/vibecompat/inet/urlencode.d
-source/dub/internal/colorize/colors.d
-source/dub/internal/colorize/cwrite.d
-source/dub/internal/colorize/package.d
-source/dub/internal/colorize/winterm.d
-source/dub/internal/logging.d
 source/dub/package_.d
 source/dub/packagemanager.d
 source/dub/packagesupplier.d
@@ -92,7 +98,12 @@ source/dub/project.d
 source/dub/recipe/io.d
 source/dub/recipe/json.d
 source/dub/recipe/packagerecipe.d
-source/dub/recipe/selection.d
 source/dub/recipe/sdl.d
+source/dub/recipe/selection.d
 source/dub/semver.d
+source/dub/test/base.d
+source/dub/test/dependencies.d
+source/dub/test/others.d
+source/dub/test/selections_from_parent_dir.d
+source/dub/test/subpackages.d
 source/dub/version_.d