diff --git a/pyls/rpc_manager.py b/pyls/rpc_manager.py
index 2bc297d6..3015a8a3 100644
--- a/pyls/rpc_manager.py
+++ b/pyls/rpc_manager.py
@@ -10,11 +10,12 @@
 from jsonrpc.exceptions import JSONRPCMethodNotFound, JSONRPCDispatchException, JSONRPCServerError
 
 log = logging.getLogger(__name__)
-
 RESPONSE_CLASS_MAP = {
     "1.0": JSONRPC10Response,
     "2.0": JSONRPC20Response
 }
+# as defined in https://github.com/Microsoft/language-server-protocol/blob/gh-pages/specification.md
+LSP_CANCEL_CODE = -32800
 
 
 class MissingMethodException(Exception):
@@ -83,7 +84,9 @@ def cancel(self, request_id):
         """
         log.debug('Cancel request %d', request_id)
         try:
-            self._received_requests[request_id].cancel()
+            self._received_requests[request_id].set_exception(
+                JSONRPCDispatchException(code=LSP_CANCEL_CODE, message="Request cancelled")
+            )
         except KeyError:
             log.debug('Received cancel for finished/nonexistent request %d', request_id)