diff --git a/src/shadowbox/server/manager_metrics.ts b/src/shadowbox/server/manager_metrics.ts
index 22414e33d..7b2b7219d 100644
--- a/src/shadowbox/server/manager_metrics.ts
+++ b/src/shadowbox/server/manager_metrics.ts
@@ -90,11 +90,11 @@ export class PrometheusManagerMetrics implements ManagerMetrics {
         asn: parseInt(entry.metric['asn']),
         asOrg: entry.metric['asorg'],
         tunnelTime: {
-          seconds: tunnelTimeByLocation.result.find((entry) => {
+          seconds: tunnelTimeByLocation.result.find((target) => {
             return (
-              entry.metric['location'] === entry.metric['location'] &&
-              entry.metric['asn'] === entry.metric['asn'] &&
-              entry.metric['asorg'] === entry.metric['asorg']
+              entry.metric['location'] === target.metric['location'] &&
+              entry.metric['asn'] === target.metric['asn'] &&
+              entry.metric['asorg'] === target.metric['asorg']
             );
           }),
         },
@@ -109,8 +109,8 @@ export class PrometheusManagerMetrics implements ManagerMetrics {
       accessKeys.push({
         accessKeyId: parseInt(entry.metric['access_key']),
         tunnelTime: {
-          seconds: tunnelTimeByAccessKey.result.find((entry) => {
-            return entry.metric['access_key'] === entry.metric['access_key'];
+          seconds: tunnelTimeByAccessKey.result.find((target) => {
+            return entry.metric['access_key'] === target.metric['access_key'];
           }),
         },
         dataTransferred: {
diff --git a/src/shadowbox/server/manager_service.ts b/src/shadowbox/server/manager_service.ts
index 28a729294..c14deb69f 100644
--- a/src/shadowbox/server/manager_service.ts
+++ b/src/shadowbox/server/manager_service.ts
@@ -613,7 +613,9 @@ export class ShadowsocksManagerService {
       logging.debug(`getServerMetrics request ${JSON.stringify(req.params)}`);
 
       if (!req.query?.since) {
-        throw new TypeError("Missing 'since' parameter. Must be an ISO timestamp");
+        return next(
+          new restifyErrors.MissingParameterError({statusCode: 400}, 'Parameter `since` is missing')
+        );
       }
 
       const timestamp = new Date(req.query.since as string);
@@ -621,10 +623,15 @@ export class ShadowsocksManagerService {
         !isNaN(timestamp.getTime()) && timestamp.toISOString() === req.query.since;
 
       if (!isIsoTimestamp) {
-        throw new TypeError(`'since' parameter must be an ISO timestamp. Got ${req.query.since}`);
+        return next(
+          new restifyErrors.InvalidArgumentError(
+            {statusCode: 400},
+            `'since' parameter must be an ISO timestamp. Got ${req.query.since}`
+          )
+        );
       }
 
-      const hours = Math.floor(new Date().getTime() - timestamp.getTime() / (1000 * 60 * 60));
+      const hours = Math.floor((new Date().getTime() - timestamp.getTime()) / (1000 * 60 * 60));
 
       const response = await this.managerMetrics.getServerMetrics({hours});
       res.send(HttpSuccess.OK, response);