diff --git a/pulsar/client/client.py b/pulsar/client/client.py
index 88fbb245e1aa616408b2f5403bc4c2702ecde3d8..06603a4abd7243c7fb5cf34f98fbfafe563c3087 100644
--- a/pulsar/client/client.py
+++ b/pulsar/client/client.py
@@ -396,6 +396,8 @@ class MessageCoexecutionPodJobClient(BaseMessageJobClient):
             {"mountPath": "/pulsar_staging", "name": "staging-directory"},
         ]
         tool_container_image = container  # TODO: this isn't right at all...
+        if not container:
+            raise Exception("Must declare a container for kubernetes job execution.")
         pulsar_container_dict = {
             "name": "pulsar-container",
             "image": pulsar_container_image,