diff --git a/tensorrt_llm/executor/proxy.py b/tensorrt_llm/executor/proxy.py
index 11451bad5b67..b1a70d444e7d 100644
--- a/tensorrt_llm/executor/proxy.py
+++ b/tensorrt_llm/executor/proxy.py
@@ -573,7 +573,14 @@ def mpi_done_callback(future: concurrent.futures.Future):
             raise RuntimeError(
                 "Executor worker returned error") from ready_signal
 
-        if isinstance(self.mpi_session, MpiPoolSession) and len(status) == 3:
+        # Re-import MpiPoolSession from its origin module rather than using the
+        # module-level name above: test infra (tests/test_common/session_reuse.py)
+        # monkeypatches this module's ``MpiPoolSession`` attribute to a pool-reuse
+        # factory function for bare LLM(...) tests, and isinstance() against a
+        # non-type raises TypeError.
+        from ..llmapi.mpi_session import MpiPoolSession as _MpiPoolSessionCls
+        if isinstance(self.mpi_session,
+                      _MpiPoolSessionCls) and len(status) == 3:
             worker_process_identities: List[WorkerProcessIdentity] = status[2]
             self._worker_process_monitor.register(worker_process_identities)