diff --git a/lib/internal/test_runner/mock/mock_timers.js b/lib/internal/test_runner/mock/mock_timers.js
index 94f9f00dee7c110..407a671eda7a8cd 100644
--- a/lib/internal/test_runner/mock/mock_timers.js
+++ b/lib/internal/test_runner/mock/mock_timers.js
@@ -265,7 +265,7 @@ class MockTimers {
       id: timerId,
       callback,
       runAt: this.#now + delay,
-      interval: isInterval,
+      interval: isInterval ? delay : undefined,
       args,
     });
 
@@ -621,7 +621,7 @@ class MockTimers {
 
       this.#executionQueue.shift();
 
-      if (timer.interval) {
+      if (timer.interval !== undefined) {
         timer.runAt += timer.interval;
         this.#executionQueue.insert(timer);
       }