diff --git a/local.c b/local.c
index 82f8fb0..5e75624 100644
--- a/local.c
+++ b/local.c
@@ -144,6 +144,8 @@ calculate_sys_precision(void)
     best *= 2;
   }
 
+  assert(precision_log >= -30);
+
   DEBUG_LOG(LOGF_Local, "Clock precision %.9f (%d)", precision_quantum, precision_log);
 }