diff --git a/python/ray/rllib/agents/a3c/a3c.py b/python/ray/rllib/agents/a3c/a3c.py
index c269df2fc6e57..d320b96368810 100644
--- a/python/ray/rllib/agents/a3c/a3c.py
+++ b/python/ray/rllib/agents/a3c/a3c.py
@@ -48,6 +48,10 @@ def get_policy_class(config):
 def validate_config(config):
     if config["entropy_coeff"] < 0:
         raise DeprecationWarning("entropy_coeff must be >= 0")
+    if config["sample_async"] and config["use_pytorch"]:
+        raise ValueError(
+            "The sample_async option is not supported with use_pytorch: "
+            "Multithreading can be lead to crashes if used with pytorch.")
 
 
 def make_async_optimizer(workers, config):