diff --git a/artiq/test/libartiq_support/artiq_time.c b/artiq/test/libartiq_support/artiq_time.c
index 07c81c9ac..18de56424 100644
--- a/artiq/test/libartiq_support/artiq_time.c
+++ b/artiq/test/libartiq_support/artiq_time.c
@@ -5,7 +5,7 @@ int64_t now = 0;
 
 int watchdog_set(long long ms)
 {
-  printf("watchdog_set %d\n", ms);
+  printf("watchdog_set %lld\n", ms);
   return ms;
 }