diff --git a/Dockerfile b/Dockerfile
index 1c6a9eb..8010409 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,7 +4,7 @@ ARG APP_VERSION
 
 ENV PYTHONDONTWRITEBYTECODE=1 \
     PYTHONUNBUFFERED=1 \
-    APP_VERSION=${APP_VERSION}
+    BERT_BUILD_VERSION=${APP_VERSION}
 
 WORKDIR /app
 COPY requirements.txt .
diff --git a/README.md b/README.md
index a568629..faaa6ed 100644
--- a/README.md
+++ b/README.md
@@ -97,6 +97,10 @@ ADMIN_PASSWORD=replace-with-a-long-unique-password
 APP_SECRET_KEY=replace-with-the-generated-secret
 ```
 
+Do not set `APP_VERSION` in `.env`. Release versions are embedded into the
+container image at build time; a runtime override can otherwise make the UI
+report a stale version.
+
 Start Bert:
 
 ```bash
diff --git a/app/version.py b/app/version.py
index 2779f2c..33aad4c 100644
--- a/app/version.py
+++ b/app/version.py
@@ -2,4 +2,6 @@
 
 
 DEFAULT_VERSION = "17.2.2"
-VERSION = (os.getenv("APP_VERSION") or DEFAULT_VERSION).removeprefix("v")
+VERSION = (
+    os.getenv("BERT_BUILD_VERSION") or os.getenv("APP_VERSION") or DEFAULT_VERSION
+).removeprefix("v")
diff --git a/tests/test_release_container.py b/tests/test_release_container.py
index 45d1b37..b1fbd48 100644
--- a/tests/test_release_container.py
+++ b/tests/test_release_container.py
@@ -26,7 +26,7 @@ def test_release_workflow_uses_release_tag_as_application_version():
 def test_container_exposes_release_version_to_application():
     dockerfile = Path("Dockerfile").read_text(encoding="utf-8")
     assert "ARG APP_VERSION" in dockerfile
-    assert "APP_VERSION=${APP_VERSION}" in dockerfile
+    assert "BERT_BUILD_VERSION=${APP_VERSION}" in dockerfile
 
 
 def test_application_version_uses_release_build_version(monkeypatch):
@@ -36,9 +36,18 @@ def test_application_version_uses_release_build_version(monkeypatch):
     assert runpy.run_path("app/version.py")["VERSION"] == "23.4.5"
 
 
+def test_baked_release_version_wins_over_stale_runtime_override(monkeypatch):
+    import runpy
+
+    monkeypatch.setenv("BERT_BUILD_VERSION", "v24.0.0")
+    monkeypatch.setenv("APP_VERSION", "v19.1.3")
+    assert runpy.run_path("app/version.py")["VERSION"] == "24.0.0"
+
+
 def test_application_version_keeps_source_fallback(monkeypatch):
     import runpy
 
+    monkeypatch.delenv("BERT_BUILD_VERSION", raising=False)
     monkeypatch.delenv("APP_VERSION", raising=False)
     assert runpy.run_path("app/version.py")["VERSION"] == "17.2.2"