diff --git a/ssb/api.py b/ssb/api.py
index cd51929..605609d 100644
--- a/ssb/api.py
+++ b/ssb/api.py
@@ -22,8 +22,8 @@ class MuxRPCSourceHandler(object):
 
 class MuxRPCSinkHandlerMixin(object):
 
-    def send(self, msg, msg_type=PSMessageType.JSON):
-        self.connection.send(msg, stream=True, msg_type=msg_type, req=self.req)
+    def send(self, msg, msg_type=PSMessageType.JSON, end=False):
+        self.connection.send(msg, stream=True, msg_type=msg_type, req=self.req, end_err=end)
 
 
 class MuxRPCDuplexHandler(MuxRPCSinkHandlerMixin, MuxRPCSourceHandler):
diff --git a/test_client.py b/test_client.py
index 2cb1744..1b6f8b0 100644
--- a/test_client.py
+++ b/test_client.py
@@ -47,7 +47,12 @@ async def main():
     handler.send(struct.pack('l', int(time.time() * 1000)), msg_type=PSMessageType.BUFFER)
     async for msg in handler:
         print('> RESPONSE:', msg)
+        handler.send(True, end=True)
+        break
 
+    handler = api.call('blobs.add', [], 'sink')
+    handler.send(b'dead0beef', msg_type=PSMessageType.BUFFER)
+    handler.send(True, end=True)
 
 # create console handler and set level to debug
 ch = logging.StreamHandler()