diff --git a/artiq/examples/kc705_nist_clock/repository/dds_setter.py b/artiq/examples/kc705_nist_clock/repository/dds_setter.py
index c5490d6b2..7f4b1447e 100644
--- a/artiq/examples/kc705_nist_clock/repository/dds_setter.py
+++ b/artiq/examples/kc705_nist_clock/repository/dds_setter.py
@@ -25,6 +25,7 @@ class DDSSetter(EnvExperiment):
 
     @kernel
     def set_dds(self, dds, frequency):
+        self.core.break_realtime()
         dds.set(frequency)
         delay(200*ms)