diff --git a/pyproject.toml b/pyproject.toml
index 2ab5295..68d81aa 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -104,11 +104,12 @@ follow_imports = "skip"
 #
 # Version is mirrored here (rather than read dynamically) because Briefcase resolves PEP621
 # `dynamic = ["version"]` by running the PEP517 build backend in an isolated env, which is wasteful
-# in CI. Bump both this string and src/searchmob_desktop/version.py together at release time.
+# in CI. Bump both this string and src/searchmob_desktop/version.py together at release time;
+# `tests/test_version_consistency.py` fails the build if they ever drift apart.
 [tool.briefcase]
 project_name = "SearchMob Desktop"
 bundle = "com.flintwave"
-version = "26.06.05"
+version = "26.06.06"
 url = "https://github.com/FlintWave/SearchMob-Desktop"
 author = "FlintWave"
 author_email = "flintwave@tuta.com"
diff --git a/tests/test_version_consistency.py b/tests/test_version_consistency.py
new file mode 100644
index 0000000..7f5868e
--- /dev/null
+++ b/tests/test_version_consistency.py
@@ -0,0 +1,27 @@
+"""The app version lives in two places that MUST agree: `src/searchmob_desktop/version.py` (the
+single source of truth, read by hatchling and the in-app update check) and the `[tool.briefcase]`
+`version` in `pyproject.toml` (mirrored there because Briefcase resolves a PEP 621 dynamic version
+by running the build backend in an isolated env, which is wasteful in CI).
+
+If they drift, the installers Briefcase builds carry a different version than the app reports, so a
+release can ship packages labelled with the previous version and Linux package managers refuse the
+upgrade. This test fails the build when that happens, so the two can never silently diverge again.
+"""
+
+from __future__ import annotations
+
+import tomllib
+from pathlib import Path
+
+from searchmob_desktop.version import __version__
+
+_PYPROJECT = Path(__file__).resolve().parent.parent / "pyproject.toml"
+
+
+def test_briefcase_version_matches_version_py() -> None:
+    data = tomllib.loads(_PYPROJECT.read_text(encoding="utf-8"))
+    briefcase_version = data["tool"]["briefcase"]["version"]
+    assert briefcase_version == __version__, (
+        f"pyproject [tool.briefcase] version {briefcase_version!r} != "
+        f"version.py {__version__!r}; bump both together at release time."
+    )