diff --git a/pyproject.toml b/pyproject.toml
index a184c8b..e4535dd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,6 +8,11 @@ dependencies = [
     "requests>=2.31.0",
 ]
 
+# Without this, setuptools' flat-layout auto-discovery treats the Flutter
+# app/ directory as a second top-level package and refuses to build.
+[tool.setuptools.packages.find]
+include = ["diet_guard*"]
+
 [tool.ruff]
 target-version = "py310"
 include = ["*.py", "**/*.py"]