diff --git a/contrib/plugins/helloworld.py b/contrib/plugins/helloworld.py
index 1a5ede345676..3fb15ca0ef1a 100755
--- a/contrib/plugins/helloworld.py
+++ b/contrib/plugins/helloworld.py
@@ -19,6 +19,12 @@ def hello(plugin, name="world"):
     return s
 
 
+@plugin.method("bye")
+def bye(plugin, name, **kwargs):
+    """This methods requires {name} to be set by the caller !"""
+    return "Bye {}".format(name)
+
+
 @plugin.init()
 def init(options, configuration, plugin, **kwargs):
     plugin.log("Plugin helloworld.py initialized")
diff --git a/contrib/pyln-client/pyln/client/plugin.py b/contrib/pyln-client/pyln/client/plugin.py
index 0446300a625e..a2315217aaeb 100644
--- a/contrib/pyln-client/pyln/client/plugin.py
+++ b/contrib/pyln-client/pyln/client/plugin.py
@@ -83,9 +83,12 @@ def set_exception(self, exc):
         self._write_result({
             'jsonrpc': '2.0',
             'id': self.id,
-            "error": "Error while processing {method}: {exc}".format(
-                method=self.method, exc=repr(exc)
-            ),
+            "error": {
+                "code": -32600,  # "Invalid Request"
+                "message": "Error while processing {method}: {exc}"
+                           .format(method=self.method, exc=repr(exc)),
+                # 'data' field "may be omitted."
+            },
         })
 
     def _write_result(self, result):
diff --git a/tests/test_plugin.py b/tests/test_plugin.py
index f1cbc2e06dcb..f8d37ebe4256 100644
--- a/tests/test_plugin.py
+++ b/tests/test_plugin.py
@@ -180,6 +180,11 @@ def test_rpc_passthrough(node_factory):
     with pytest.raises(RpcError):
         n.rpc.fail()
 
+    # Try to call a method without enough arguments
+    with pytest.raises(RpcError, match="error: {'code': -32600, 'message': "
+                                       "'Error while processing bye"):
+        n.rpc.bye()
+
 
 def test_plugin_dir(node_factory):
     """--plugin-dir works"""