diff --git a/simvue/factory/proxy/offline.py b/simvue/factory/proxy/offline.py
index 7cd24926..add39c14 100644
--- a/simvue/factory/proxy/offline.py
+++ b/simvue/factory/proxy/offline.py
@@ -203,7 +203,7 @@ def send_heartbeat(self) -> typing.Optional[dict[str, typing.Any]]:
         logger.debug(
             f"Creating heartbeat file: {os.path.join(self._directory, 'heartbeat')}"
         )
-        pathlib.Path(os.path.join(self._directory, "heartbeat"), "a").touch()
+        pathlib.Path(os.path.join(self._directory, "heartbeat")).touch()
         return {"success": True}
 
     @skip_if_failed("_aborted", "_suppress_errors", False)