diff -uprb python-jsonrpc-server-0.2.0.orig/pyls_jsonrpc/endpoint.py python-jsonrpc-server-0.2.0/pyls_jsonrpc/endpoint.py
--- python-jsonrpc-server-0.2.0.orig/pyls_jsonrpc/endpoint.py	2019-06-27 18:42:22.000000000 +0300
+++ python-jsonrpc-server-0.2.0/pyls_jsonrpc/endpoint.py	2019-11-02 23:24:59.407851208 +0200
@@ -98,7 +98,7 @@ class Endpoint(object):
             message (dict): The JSON RPC message sent by the client
         """
         if 'jsonrpc' not in message or message['jsonrpc'] != JSONRPC_VERSION:
-            log.warn("Unknown message type %s", message)
+            log.warning("Unknown message type %s", message)
             return
 
         if 'id' not in message:
@@ -135,7 +135,7 @@ class Endpoint(object):
         try:
             handler = self._dispatcher[method]
         except KeyError:
-            log.warn("Ignoring notification for unknown method %s", method)
+            log.warning("Ignoring notification for unknown method %s", method)
             return
 
         try:
@@ -165,7 +165,7 @@ class Endpoint(object):
         request_future = self._client_request_futures.pop(msg_id, None)
 
         if not request_future:
-            log.warn("Received cancel notification for unknown message id %s", msg_id)
+            log.warning("Received cancel notification for unknown message id %s", msg_id)
             return
 
         # Will only work if the request hasn't started executing
@@ -230,12 +230,13 @@ class Endpoint(object):
         request_future = self._server_request_futures.pop(msg_id, None)
 
         if not request_future:
-            log.warn("Received response to unknown message id %s", msg_id)
+            log.warning("Received response to unknown message id %s", msg_id)
             return
 
         if error is not None:
             log.debug("Received error response to message %s: %s", msg_id, error)
             request_future.set_exception(JsonRpcException.from_dict(error))
+            return
 
         log.debug("Received result for message %s: %s", msg_id, result)
         request_future.set_result(result)
diff -uprb python-jsonrpc-server-0.2.0.orig/test/test_endpoint.py python-jsonrpc-server-0.2.0/test/test_endpoint.py
--- python-jsonrpc-server-0.2.0.orig/test/test_endpoint.py	2019-06-27 18:42:22.000000000 +0300
+++ python-jsonrpc-server-0.2.0/test/test_endpoint.py	2019-11-02 23:24:21.033838729 +0200
@@ -115,9 +115,9 @@ def test_request_cancel(endpoint, consum
         'params': {'id': MSG_ID}
     })
 
-    with pytest.raises(exceptions.JsonRpcException) as exc_info:
+    with pytest.raises((exceptions.JsonRpcException, futures.CancelledError)) as exc_info:
         assert future.result(timeout=2)
-    assert exc_info.type == exceptions.JsonRpcRequestCancelled
+    assert exc_info.type in (exceptions.JsonRpcRequestCancelled, futures.CancelledError)
 
 
 def test_consume_notification(endpoint, dispatcher):