diff --git a/src/Clock.ts b/src/Clock.ts
index b9f5fbc..3b3cffb 100644
--- a/src/Clock.ts
+++ b/src/Clock.ts
@@ -294,6 +294,7 @@ export class Clock {
      *
      * @returns deviation between the logical time and the real time
      */
+    if(this.afterEvaluation<this.lastPulseAt) return 0;
     return (this.afterEvaluation - this.lastPulseAt) / 1000;
   }