diff --git a/src/py/flwr/cli/run/run.py b/src/py/flwr/cli/run/run.py
index 05c4bf183dda..5696533a8f14 100644
--- a/src/py/flwr/cli/run/run.py
+++ b/src/py/flwr/cli/run/run.py
@@ -187,7 +187,7 @@ def _run_with_exec_api(
     if output_format == CliOutputFormat.JSON:
         run_output = json.dumps(
             {
-                "success": "true" if res.HasField("run_id") else "false",
+                "success": res.HasField("run_id"),
                 "run-id": res.run_id if res.HasField("run_id") else None,
                 "fab-id": fab_id,
                 "fab-name": fab_id.rsplit("/", maxsplit=1)[-1],