diff --git a/check-linuxcnc-browser-app-source-map.sh b/check-linuxcnc-browser-app-source-map.sh
index f173695..f183310 100755
--- a/check-linuxcnc-browser-app-source-map.sh
+++ b/check-linuxcnc-browser-app-source-map.sh
@@ -121,4 +121,10 @@ for entry in [
 app = Path("web/src/app.js").read_text(encoding="utf-8")
 if "parse(" in app.replace("parseProgram", ""):
     raise SystemExit("browser app should route program execution through parseFileWithParameterFile, not direct parse")
+if app.count("elements.backendSelect.value = linuxCncBackend;") != 2:
+    raise SystemExit("browser app backend selector must only be forced to the LinuxCNC backend")
+if "backendSelect.value" in app.replace("elements.backendSelect.value = linuxCncBackend;", ""):
+    raise SystemExit("browser app must not read the backend selector as a dynamic backend source")
+if 'backend: linuxCncBackend' not in app:
+    raise SystemExit("browser app parse options must force the LinuxCNC backend")
 PY
diff --git a/docs/linuxcnc-browser-app-source-map.md b/docs/linuxcnc-browser-app-source-map.md
index 822e8e4..46f8c68 100644
--- a/docs/linuxcnc-browser-app-source-map.md
+++ b/docs/linuxcnc-browser-app-source-map.md
@@ -37,6 +37,8 @@ must not expand the temporary smoke parser.
 - The app must require OPFS for browser program parsing and call
   `parseFileWithParameterFile(programPath, parameterPath, "linuxcnc", ...)`.
 - The visible backend selector must stay limited to the LinuxCNC RS274 backend.
+- The app must not read the backend selector as a dynamic backend source; it
+  must force `linuxCncBackend` for browser parsing.
 - `test-native.sh`, `test-linuxcnc-source-link.sh`, and `build-wasm.sh` must
   run `./check-linuxcnc-browser-app-source-map.sh` before consuming app-backed
   browser artifacts or source-linked LinuxCNC objects.