diff --git a/index.js b/index.js
index 5e7687c..4342685 100644
--- a/index.js
+++ b/index.js
@@ -88,7 +88,8 @@ const middlewareWrapper = (app, config) => {
   config.spans.forEach((span) => {
     span.os = []
     span.responses = []
-    setInterval(() => gatherOsMetrics(io, span), span.interval * 1000)
+    const interval = setInterval(() => gatherOsMetrics(io, span), span.interval * 1000)
+    interval.unref()
   })
   // console.log(config)
 
diff --git a/koa-monitor-frontend.js b/koa-monitor-frontend.js
index 2883315..474896c 100644
--- a/koa-monitor-frontend.js
+++ b/koa-monitor-frontend.js
@@ -175,9 +175,11 @@ socket.on('stats', function (data) {
     responseTimeChart.data.labels.push(data.responses.timestamp)
 
     var deltaTime = data.responses.timestamp - rpsChart.data.labels[rpsChart.data.labels.length - 1]
-    rpsStat.textContent = (data.responses.count / deltaTime * 1000).toFixed(2)
-    rpsChart.data.datasets[0].data.push(data.responses.count / deltaTime * 1000)
-    rpsChart.data.labels.push(data.responses.timestamp)
+    if (deltaTime > 0) {
+      rpsStat.textContent = (data.responses.count / deltaTime * 1000).toFixed(2)
+      rpsChart.data.datasets[0].data.push(data.responses.count / deltaTime * 1000)
+      rpsChart.data.labels.push(data.responses.timestamp)
+    }
 
     charts.forEach(function (chart) {
       if (spans[defaultSpan].retention < chart.data.labels.length) {
diff --git a/package.json b/package.json
index 151bc57..a543961 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "koa-monitor",
-  "version": "0.2.3",
+  "version": "0.2.4",
   "description": "Realtime monitoring for koa-based Node applications",
   "main": "index.js",
   "keywords": [
@@ -10,6 +10,9 @@
     "koa",
     "charts"
   ],
+  "engines" : {
+    "node" : ">=4"
+  },
   "author": "Jiri Spac capajj@gmail.com",
   "license": "MIT",
   "repository": {
@@ -19,11 +22,11 @@
   "dependencies": {
     "handlebars": "^4.0.5",
     "mz": "^2.4.0",
-    "pidusage": "^1.0.4",
+    "pidusage": "^1.0.5",
     "socket.io": "^1.4.8"
   },
   "devDependencies": {
-    "koa": "^1.2.1",
-    "standard": "^8.0.0-beta.5"
+    "koa": "^1.2.2",
+    "standard": "^8.0.0"
   }
 }