diff --git a/contrib/pyln-client/pyln/client/plugin.py b/contrib/pyln-client/pyln/client/plugin.py
index d14ae5d3c8bc..59d99bf7886a 100644
--- a/contrib/pyln-client/pyln/client/plugin.py
+++ b/contrib/pyln-client/pyln/client/plugin.py
@@ -217,13 +217,15 @@ def __init__(self, stdout: Optional[io.TextIOBase] = None,
                  dynamic: bool = True,
                  init_features: Optional[Union[int, str, bytes]] = None,
                  node_features: Optional[Union[int, str, bytes]] = None,
-                 invoice_features: Optional[Union[int, str, bytes]] = None):
+                 invoice_features: Optional[Union[int, str, bytes]] = None,
+                 custom_msgs: Optional[List[int]] = None):
         self.methods = {
             'init': Method('init', self._init, MethodType.RPCMETHOD)
         }
 
         self.options: Dict[str, Dict[str, Any]] = {}
         self.notification_topics: List[str] = []
+        self.custom_msgs = custom_msgs
 
         def convert_featurebits(
                 bits: Optional[Union[int, str, bytes]]) -> Optional[str]:
@@ -931,6 +933,9 @@ def _getmanifest(self, **kwargs) -> JSONType:
         if features is not None:
             manifest['featurebits'] = features
 
+        if self.custom_msgs is not None:
+            manifest['custommessages'] = self.custom_msgs
+
         return manifest
 
     def _init(self, options: Dict[str, JSONType],
diff --git a/tests/plugins/allow_even_msgs.py b/tests/plugins/allow_even_msgs.py
new file mode 100755
index 000000000000..b45c110d2b3b
--- /dev/null
+++ b/tests/plugins/allow_even_msgs.py
@@ -0,0 +1,13 @@
+#!/usr/bin/env python3
+from pyln.client import Plugin
+
+plugin = Plugin(custom_msgs=[43690])
+
+
+@plugin.hook('custommsg')
+def on_custommsg(peer_id, payload, plugin, message=None, **kwargs):
+    plugin.log("Got message {}".format(int(payload[:4], 16)))
+    return {'result': 'continue'}
+
+
+plugin.run()
diff --git a/tests/test_misc.py b/tests/test_misc.py
index ee59d5b7fa04..9d39f26bc15a 100644
--- a/tests/test_misc.py
+++ b/tests/test_misc.py
@@ -3626,3 +3626,35 @@ def test_setconfig(node_factory, bitcoind):
         assert lines[1].startswith('# Inserted by setconfig ')
         assert lines[2] == 'min-capacity-sat=400000'
         assert len(lines) == 3
+
+
+def test_even_sendcustommsg(node_factory):
+    l1, l2 = node_factory.get_nodes(2, opts={'log-level': 'io'})
+    l1.connect(l2)
+
+    # Even-numbered message
+    msg = hex(43690)[2:] + ('ff' * 30) + 'bb'
+
+    # l2 will hang up when it gets this.
+    l1.rpc.sendcustommsg(l2.info['id'], msg)
+    l2.daemon.wait_for_log(r'\[IN\] {}'.format(msg))
+    l1.daemon.wait_for_log('Invalid unknown even msg')
+    wait_for(lambda: l1.rpc.listpeers(l2.info['id'])['peers'] == [])
+
+    # Now with a plugin which allows it
+    l1.connect(l2)
+    l2.rpc.plugin_start(os.path.join(os.getcwd(), "tests/plugins/allow_even_msgs.py"))
+
+    l1.rpc.sendcustommsg(l2.info['id'], msg)
+    l2.daemon.wait_for_log(r'\[IN\] {}'.format(msg))
+    l2.daemon.wait_for_log(r'allow_even_msgs.*Got message 43690')
+
+    # And nobody gets upset
+    assert only_one(l1.rpc.listpeers(l2.info['id'])['peers'])['connected']
+
+    # It does if we remove the plugin though!
+    l2.rpc.plugin_stop("allow_even_msgs.py")
+    l1.rpc.sendcustommsg(l2.info['id'], msg)
+    l2.daemon.wait_for_log(r'\[IN\] {}'.format(msg))
+    l1.daemon.wait_for_log('Invalid unknown even msg')
+    wait_for(lambda: l1.rpc.listpeers(l2.info['id'])['peers'] == [])