diff --git a/app/vmalert/rule/alerting.go b/app/vmalert/rule/alerting.go
index be50ef1335..da013ec106 100644
--- a/app/vmalert/rule/alerting.go
+++ b/app/vmalert/rule/alerting.go
@@ -440,14 +440,13 @@ func (ar *AlertingRule) exec(ctx context.Context, ts time.Time, limit int) ([]pr
 			a.KeepFiringSince = time.Time{}
 			continue
 		}
-		a, err := ar.newAlert(m, ls, start, qFn)
+		a, err := ar.newAlert(m, ls, ts, qFn)
 		if err != nil {
 			curState.Err = fmt.Errorf("failed to create alert: %w", err)
 			return nil, curState.Err
 		}
 		a.ID = h
 		a.State = notifier.StatePending
-		a.ActiveAt = ts
 		ar.alerts[h] = a
 		ar.logDebugf(ts, a, "created in state PENDING")
 	}
@@ -473,7 +472,7 @@ func (ar *AlertingRule) exec(ctx context.Context, ts time.Time, limit int) ([]pr
 				}
 				// alerts with ar.KeepFiringFor>0 may remain FIRING
 				// even if their expression isn't true anymore
-				if ts.Sub(a.KeepFiringSince) > ar.KeepFiringFor {
+				if ts.Sub(a.KeepFiringSince) >= ar.KeepFiringFor {
 					a.State = notifier.StateInactive
 					a.ResolvedAt = ts
 					ar.logDebugf(ts, a, "FIRING => INACTIVE: is absent in current evaluation round")
diff --git a/app/vmalert/rule/alerting_test.go b/app/vmalert/rule/alerting_test.go
index 5b7fb54045..95539efd49 100644
--- a/app/vmalert/rule/alerting_test.go
+++ b/app/vmalert/rule/alerting_test.go
@@ -328,14 +328,17 @@ func TestAlertingRule_Exec(t *testing.T) {
 			fq := &datasource.FakeQuerier{}
 			tc.rule.q = fq
 			tc.rule.GroupID = fakeGroup.ID()
+			ts := time.Now()
 			for i, step := range tc.steps {
 				fq.Reset()
 				fq.Add(step...)
-				if _, err := tc.rule.exec(context.TODO(), time.Now(), 0); err != nil {
+				if _, err := tc.rule.exec(context.TODO(), ts, 0); err != nil {
 					t.Fatalf("unexpected err: %s", err)
 				}
-				// artificial delay between applying steps
-				time.Sleep(defaultStep)
+
+				// shift the execution timestamp before the next iteration
+				ts = ts.Add(defaultStep)
+
 				if _, ok := tc.expAlerts[i]; !ok {
 					continue
 				}