diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 1b350afc2..42c9c362a 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "3.15.17",
+    "version": "3.15.18",
     "bin": "bin/hydrooj.js",
     "main": "src/loader",
     "module": "src/loader",
diff --git a/packages/hydrooj/src/service/server.ts b/packages/hydrooj/src/service/server.ts
index 369c2b49c..df14af2ce 100644
--- a/packages/hydrooj/src/service/server.ts
+++ b/packages/hydrooj/src/service/server.ts
@@ -416,9 +416,10 @@ export function Connection(
                 };
             }
             conn.onclose = () => {
-                h.cleanup?.(args);
                 bus.emit('connection/close', h);
+                h.cleanup?.(args);
             };
+            bus.emit('connection/active', h);
         } catch (e) {
             await h.onerror(e);
         }
diff --git a/packages/prom-client/metrics.ts b/packages/prom-client/metrics.ts
index a66ff8161..e8483eeb2 100644
--- a/packages/prom-client/metrics.ts
+++ b/packages/prom-client/metrics.ts
@@ -8,7 +8,7 @@ export const registry = new Registry();
 registry.setDefaultLabels({ instanceid: process.env.NODE_APP_INSTANCE });
 function createMetric<Q extends string, T extends (new (a: any) => Metric<Q>)>(
     C: T, name: string, help: string, extra?: T extends new (a: infer R) => any ? Partial<R> : never,
-): T extends new (a) => Counter<Q> ? Counter<Q> : T extends new (a) => Gauge<Q> ? Gauge<Q> : Metric<Q> {
+): T extends (new (a) => Gauge<Q>) ? Gauge<Q> : T extends (new (a) => Counter<Q>) ? Counter<Q> : Metric<Q> {
     const metric = new C({ name, help, ...(extra || {}) });
     registry.registerMetric(metric);
     return metric as any;
@@ -38,11 +38,11 @@ bus.on('handler/after/ProblemSubmit', (that) => {
 const connectionGauge = createMetric(Gauge, 'hydro_connection', 'connectioncount', {
     labelNames: ['domainId'],
 });
-bus.on('connection/create', (h) => {
+bus.on('connection/active', (h) => {
     connectionGauge.inc({ domainId: h.args.domainId });
 });
 bus.on('connection/close', (h) => {
-    connectionGauge.inc({ domainId: h.args.domainId }, -1);
+    connectionGauge.dec({ domainId: h.args.domainId });
 });
 
 const taskColl = db.collection('task');
diff --git a/packages/prom-client/package.json b/packages/prom-client/package.json
index 819400e33..3e5c576da 100644
--- a/packages/prom-client/package.json
+++ b/packages/prom-client/package.json
@@ -1,6 +1,6 @@
 {
     "name": "@hydrooj/prom-client",
-    "version": "0.0.2",
+    "version": "0.0.3",
     "dependencies": {
         "prom-client": "^14.0.1"
     }