diff --git a/lightningd/peer_control.c b/lightningd/peer_control.c
index d674ba5f1..3de82c74a 100644
--- a/lightningd/peer_control.c
+++ b/lightningd/peer_control.c
@@ -2404,6 +2404,16 @@ static struct command_result *json_sendcustommsg(struct command *cmd,
 		    type, wire_type_name(type));
 	}
 
+	if (type % 2 == 0) {
+		return command_fail(
+		    cmd, JSONRPC2_INVALID_REQUEST,
+		    "Cannot send even-typed %d custom message. Currently "
+		    "custom messages are limited to odd-numbered message "
+		    "types, as even-numbered types might result in "
+		    "disconnections.",
+		    type);
+	}
+
 	peer = peer_by_id(cmd->ld, dest);
 	if (!peer) {
 		return command_fail(cmd, JSONRPC2_INVALID_REQUEST,
diff --git a/tests/test_misc.py b/tests/test_misc.py
index 648374fa7..fe2bd5a65 100644
--- a/tests/test_misc.py
+++ b/tests/test_misc.py
@@ -2096,6 +2096,12 @@ def test_sendcustommsg(node_factory):
     with pytest.raises(RpcError, match=r'Cannot send messages of type 18 .WIRE_PING.'):
         l2.rpc.dev_sendcustommsg(l2.info['id'], r'0012')
 
+    # The sendcustommsg RPC call is currently limited to odd-typed messages,
+    # since they will not result in disconnections or even worse channel
+    # failures.
+    with pytest.raises(RpcError, match=r'Cannot send even-typed [0-9]+ custom message'):
+        l2.rpc.dev_sendcustommsg(l2.info['id'], r'00FE')
+
     # This should work since the peer is currently owned by `channeld`
     l2.rpc.dev_sendcustommsg(l1.info['id'], msg)
     l2.daemon.wait_for_log(