diff --git a/ml-agents/mlagents/trainers/torch/model_serialization.py b/ml-agents/mlagents/trainers/torch/model_serialization.py
index b82e9005d4..e9a4dfc9f4 100644
--- a/ml-agents/mlagents/trainers/torch/model_serialization.py
+++ b/ml-agents/mlagents/trainers/torch/model_serialization.py
@@ -19,14 +19,20 @@ class exporting_to_onnx:
     This implementation is thread safe.
     """
 
+    # local is_exporting flag for each thread
     _local_data = threading.local()
     _local_data._is_exporting = False
 
+    # global lock shared among all threads, to make sure only one thread is exporting at a time
+    _lock = threading.Lock()
+
     def __enter__(self):
+        self._lock.acquire()
         self._local_data._is_exporting = True
 
     def __exit__(self, *args):
         self._local_data._is_exporting = False
+        self._lock.release()
 
     @staticmethod
     def is_exporting():