diff --git a/build-linuxcnc-wasm-standalone-probe.sh b/build-linuxcnc-wasm-standalone-probe.sh
index 7cebf80..87a68e8 100755
--- a/build-linuxcnc-wasm-standalone-probe.sh
+++ b/build-linuxcnc-wasm-standalone-probe.sh
@@ -111,6 +111,7 @@ case "$mode" in
         ;;
     python-plugin-link)
         python_plugin_shim=$(./list-linuxcnc-wasm-safe-shims.sh python_plugin.cc)
+        grep -F 'LinuxCNC source basis: src/emc/pythonplugin/python_plugin.cc and' core/wasm_shims/pythonplugin/python_plugin_probe_main.cc >/dev/null
         sources+=(
             "$python_plugin_shim"
             core/wasm_shims/pythonplugin/python_plugin_probe_main.cc
diff --git a/core/wasm_shims/pythonplugin/python_plugin_probe_main.cc b/core/wasm_shims/pythonplugin/python_plugin_probe_main.cc
index 8860bbb..bf04a28 100644
--- a/core/wasm_shims/pythonplugin/python_plugin_probe_main.cc
+++ b/core/wasm_shims/pythonplugin/python_plugin_probe_main.cc
@@ -1,5 +1,7 @@
 #include "pythonplugin/python_plugin.hh"
 
+// LinuxCNC source basis: src/emc/pythonplugin/python_plugin.cc and
+// python_plugin.hh define the PythonPlugin API exercised by this link probe.
 int main() {
     auto *plugin = PythonPlugin::instantiate(nullptr);
     if (!plugin) {