diff --git a/src/reporter.ts b/src/reporter.ts
index 9ddbedf..03756dc 100644
--- a/src/reporter.ts
+++ b/src/reporter.ts
@@ -225,7 +225,11 @@ export class RPReporter implements Reporter {
         case TASK_STATUS.fail:
           finishTestItemObj.status = state === TASK_STATUS.fail ? STATUSES.FAILED : STATUSES.PASSED;
           if (startTime && duration) {
-            finishTestItemObj.endTime = startTime + duration;
+            // duration can be a floating number with more than 3 digits after dot
+            const fixedDurationInMs = Number(duration.toFixed(3));
+            finishTestItemObj.endTime = clientHelpers.formatMicrosecondsToISOString(
+              (startTime + fixedDurationInMs) * 1000,
+            );
           }
           break;
         case TASK_MODE.skip:
diff --git a/src/types/@reportportal/client-javascript/lib/helpers.d.ts b/src/types/@reportportal/client-javascript/lib/helpers.d.ts
index 351a541..7aaf926 100644
--- a/src/types/@reportportal/client-javascript/lib/helpers.d.ts
+++ b/src/types/@reportportal/client-javascript/lib/helpers.d.ts
@@ -17,4 +17,5 @@
 
 declare module '@reportportal/client-javascript/lib/helpers' {
   export function now(): string;
+  export function formatMicrosecondsToISOString(microseconds: number): string;
 }