diff --git a/pyinfra/server/server.py b/pyinfra/server/server.py
index 8d1c06d..f8042d1 100644
--- a/pyinfra/server/server.py
+++ b/pyinfra/server/server.py
@@ -11,7 +11,7 @@ from pyinfra.server.stream.rest import LazyRestProcessor
 
 
 @singledispatch
-def set_up_processing_server(arg: Union[dict, Callable], buffer_size=1):
+def set_up_processing_server(arg: Union[dict, Callable], buffer_size):
     """Produces a processing server given a streamable function or a mapping from operations to streamable functions.
     Streamable functions are constructed by calling pyinfra.server.utils.make_streamable_and_wrap_in_packing_logic on a
     function taking a tuple of data and metadata and also returning a tuple or yielding tuples of data and metadata.
@@ -32,12 +32,12 @@ def set_up_processing_server(arg: Union[dict, Callable], buffer_size=1):
 
 
 @set_up_processing_server.register
-def _(operation2stream_fn: dict, buffer_size):
+def _(operation2stream_fn: dict, buffer_size=1):
     return __stream_fn_to_processing_server(operation2stream_fn, buffer_size)
 
 
 @set_up_processing_server.register
-def _(stream_fn: object, buffer_size):
+def _(stream_fn: object, buffer_size=1):
     operation2stream_fn = {None: stream_fn}
     return __stream_fn_to_processing_server(operation2stream_fn, buffer_size)