diff --git a/x-pack/plugins/apm/server/lib/alerts/register_transaction_duration_alert_type.test.ts b/x-pack/plugins/apm/server/lib/alerts/register_transaction_duration_alert_type.test.ts
index ec0a986e2722..43abe89a4733 100644
--- a/x-pack/plugins/apm/server/lib/alerts/register_transaction_duration_alert_type.test.ts
+++ b/x-pack/plugins/apm/server/lib/alerts/register_transaction_duration_alert_type.test.ts
@@ -59,7 +59,7 @@ describe('registerTransactionDurationAlertType', () => {
       transactionType: 'request',
       serviceName: 'opbeans-java',
       environment: 'Not defined',
-      threshold: 3000,
+      threshold: 3000000,
       triggerValue: '5,500 ms',
       interval: `5m`,
     });
diff --git a/x-pack/plugins/apm/server/lib/alerts/register_transaction_duration_alert_type.ts b/x-pack/plugins/apm/server/lib/alerts/register_transaction_duration_alert_type.ts
index fedc185d84f9..a831f94cd6b6 100644
--- a/x-pack/plugins/apm/server/lib/alerts/register_transaction_duration_alert_type.ts
+++ b/x-pack/plugins/apm/server/lib/alerts/register_transaction_duration_alert_type.ts
@@ -201,11 +201,11 @@ export function registerTransactionDurationAlertType({
               [TRANSACTION_TYPE]: alertParams.transactionType,
               [PROCESSOR_EVENT]: ProcessorEvent.transaction,
               [ALERT_EVALUATION_VALUE]: transactionDuration,
-              [ALERT_EVALUATION_THRESHOLD]: alertParams.threshold,
+              [ALERT_EVALUATION_THRESHOLD]: thresholdMicroseconds,
               [ALERT_REASON]: formatTransactionDurationReason({
                 measured: transactionDuration,
                 serviceName: alertParams.serviceName,
-                threshold: alertParams.threshold,
+                threshold: thresholdMicroseconds,
                 asDuration,
               }),
             },
@@ -214,7 +214,7 @@ export function registerTransactionDurationAlertType({
             transactionType: alertParams.transactionType,
             serviceName: alertParams.serviceName,
             environment: getEnvironmentLabel(alertParams.environment),
-            threshold: alertParams.threshold,
+            threshold: thresholdMicroseconds,
             triggerValue: transactionDurationFormatted,
             interval: `${alertParams.windowSize}${alertParams.windowUnit}`,
           });