diff --git a/sirepo/job_driver/__init__.py b/sirepo/job_driver/__init__.py
index 1c2b6b5bfe..3757162001 100644
--- a/sirepo/job_driver/__init__.py
+++ b/sirepo/job_driver/__init__.py
@@ -170,7 +170,7 @@ def receive(cls, msg):
             return
         pkdlog("unknown agent, sending kill; msg={}", msg)
         try:
-            msg.handler.write_message(PKDict(opName=job.OP_KILL))
+            msg.handler.write_message(PKDict(opName=job.OP_KILL), binary=True)
         except tornado.websocket.WebSocketClosedError:
             pkdlog("websocket closed {} from unknown agent", self)
         except Exception as e:
@@ -179,7 +179,7 @@ def receive(cls, msg):
     def send(self, op):
         pkdlog("{} {} runDir={}", self, op, op.msg.get("runDir"))
         try:
-            self._websocket.write_message(pkjson.dump_bytes(op.msg))
+            self._websocket.write_message(pkjson.dump_bytes(op.msg), binary=True)
             return True
         except tornado.websocket.WebSocketClosedError:
             pkdlog("websocket closed op={}", op)
diff --git a/sirepo/pkcli/job_agent.py b/sirepo/pkcli/job_agent.py
index b3e4330bee..bfbe758240 100644
--- a/sirepo/pkcli/job_agent.py
+++ b/sirepo/pkcli/job_agent.py
@@ -286,7 +286,7 @@ async def send(self, msg):
         try:
             if not isinstance(msg, _OpMsg):
                 raise AssertionError("expected _OpMsg type={} msg={}", type(msg), msg)
-            await self._websocket.write_message(pkjson.dump_bytes(msg))
+            await self._websocket.write_message(pkjson.dump_bytes(msg), binary=True)
             return True
         except Exception as e:
             pkdlog("exception={} msg={} stack={}", e, msg, pkdexc())