diff --git a/artiq/examples/kc705_nist_clock/repository/blink_forever.py b/artiq/examples/kc705_nist_clock/repository/blink_forever.py
index 83c589ebe..68d5e031e 100644
--- a/artiq/examples/kc705_nist_clock/repository/blink_forever.py
+++ b/artiq/examples/kc705_nist_clock/repository/blink_forever.py
@@ -1,7 +1,12 @@
 from artiq.experiment import *
+from artiq.coredevice.core import Core
+from artiq.coredevice.ttl import TTLOut
 
-
+@nac3
 class BlinkForever(EnvExperiment):
+    core: KernelInvariant[Core]
+    led: KernelInvariant[TTLOut]
+
     def build(self):
         self.setattr_device("core")
         self.setattr_device("led")
@@ -10,5 +15,5 @@ class BlinkForever(EnvExperiment):
     def run(self):
         self.core.reset()
         while True:
-            self.led.pulse(100*ms)
-            delay(100*ms)
+            self.led.pulse(100.*ms)
+            self.core.delay(100.*ms)