diff --git a/crdt-sync/pyproject.toml b/crdt-sync/pyproject.toml
index bef7f5c..060ab75 100644
--- a/crdt-sync/pyproject.toml
+++ b/crdt-sync/pyproject.toml
@@ -1,10 +1,18 @@
 [project]
 name = "crdt-sync"
-version = "0.5.0"
+version = "0.5.1"
 description = "Shared CRDT merge scheme + GitHub-Contents-API sync transport for cross-device apps"
 requires-python = ">=3.10"
 dependencies = ["requests"]
 
+# Ship only the library. `tool/` is a package too (it has an __init__.py so
+# its scripts import cleanly), and setuptools' flat-layout auto-discovery
+# refuses to build at all once it sees two top-level packages -- naming the
+# one that belongs in the wheel is what keeps `pip install` working, and
+# keeps one-shot migration scripts out of every consumer's site-packages.
+[tool.setuptools]
+packages = ["crdt_sync", "crdt_sync.tests"]
+
 [tool.ruff]
 target-version = "py310"
 include = ["*.py", "**/*.py"]