diff --git a/python/monarch/_src/actor/bootstrap_main.py b/python/monarch/_src/actor/bootstrap_main.py
index b94a8a96..053aa4bb 100644
--- a/python/monarch/_src/actor/bootstrap_main.py
+++ b/python/monarch/_src/actor/bootstrap_main.py
@@ -11,6 +11,7 @@
 import asyncio
 import importlib.resources
 import logging
+import multiprocessing
 import os
 import sys
 
@@ -63,4 +64,7 @@ def invoke_main():
 
 
 if __name__ == "__main__":
+    # Ensure that processes started via `multiprocessing` are spawned, not forked.
+    # forking is a terrible default, see: https://github.com/python/cpython/issues/84559
+    multiprocessing.set_start_method("spawn", force=True)
     invoke_main()  # pragma: no cover