diff --git a/artiq/examples/nac3devices/nac3devices.json b/artiq/examples/nac3devices/nac3devices.json
index d7285f690..99971df10 100644
--- a/artiq/examples/nac3devices/nac3devices.json
+++ b/artiq/examples/nac3devices/nac3devices.json
@@ -13,7 +13,8 @@
         {
             "type": "mirny",
             "ports": [1],
-            "clk_sel": "mmcx"
+            "clk_sel": "mmcx",
+            "refclk": 125e6
         },
         {
             "type": "urukul",