diff --git a/distributask/distributask.py b/distributask/distributask.py
index 6b43bd4..c4630f4 100644
--- a/distributask/distributask.py
+++ b/distributask/distributask.py
@@ -539,7 +539,7 @@ def create_instance(
             raise ValueError("VAST_API_KEY is not set in the environment")
 
         if command is None:
-            command = f"celery -A {module_name} worker --loglevel=info --concurrency=1 --without-heartbeat --prefetch_multiplier=1"
+            command = f"celery -A {module_name} worker --loglevel=info --concurrency=1 --without-heartbeat --prefetch-multiplier=1"
 
         if env_settings is None:
             env_settings = self.settings