diff --git a/artiq/coredevice/comm_kernel.py b/artiq/coredevice/comm_kernel.py
index 670d2cc41..7db34453c 100644
--- a/artiq/coredevice/comm_kernel.py
+++ b/artiq/coredevice/comm_kernel.py
@@ -6,7 +6,6 @@ import socket
 import re
 import linecache
 import os
-import json
 from enum import Enum
 from fractions import Fraction
 from collections import namedtuple