diff --git a/lib/clean-host.js b/lib/clean-host.js
index 4a20697..ddaa9a9 100644
--- a/lib/clean-host.js
+++ b/lib/clean-host.js
@@ -54,7 +54,9 @@ function checkTrimmingNeeded(value) {
  * @param {string} value
  */
 function checkLowerCaseNeeded(value) {
-  for (var i = 0; i < value.length; i += 1) {
+  let i = 0;
+  const m = value.length;
+  for (; i < m; i++) {
     var code = value.charCodeAt(i);
     if (code >= 65 && code <= 90) { // [A-Z]
       return true;
diff --git a/lib/is-valid.js b/lib/is-valid.js
index 811c9bb..19fcd9e 100644
--- a/lib/is-valid.js
+++ b/lib/is-valid.js
@@ -62,8 +62,13 @@ module.exports = function isValid(hostname) {
   var code;
   var len = hostname.length;
 
-  for (var i = 0; i < len; i += 1) {
+  let i = 0;
+  let hasAlphaOrDigit = false;
+  for (; i < len; i++) {
     code = hostname.charCodeAt(i);
+    const isAlphaOrDigit = isAlpha(code) || isDigit(code);
+    hasAlphaOrDigit |= isAlphaOrDigit;
+
 
     if (code === 46) { // '.'
       if (
@@ -72,14 +77,16 @@ module.exports = function isValid(hostname) {
         // Check that previous character was not already a '.'
         lastCharCode === 46 ||
         // Check that the previous label does not end with a '-'
-        lastCharCode === 45
+        lastCharCode === 45 ||
+        // check that prvious label does not end with a '_'
+        lastCharCode === 95
       ) {
         return false;
       }
 
       lastDotIndex = i;
-    } else if (!(isAlpha(code) || isDigit(code) || code === 45)) {
-      // Check if there is a forbidden character in the label: [^a-zA-Z0-9-]
+    } else if (!isAlphaOrDigit && !code === 45 && !code === 95) {
+      // Check if there is a forbidden character in the label: [^a-zA-Z0-9-_]
       return false;
     }
 
@@ -87,6 +94,8 @@ module.exports = function isValid(hostname) {
   }
 
   return (
+    // has atleast 1 digit or alpha character
+    hasAlphaOrDigit &&
     // Check that last label is shorter than 63 chars
     (len - lastDotIndex - 1) <= 63 &&
     // Check that the last character is an allowed trailing label character.
diff --git a/package.json b/package.json
index 106e274..5d5faf5 100644
--- a/package.json
+++ b/package.json
@@ -47,9 +47,7 @@
     ]
   },
   "dependencies": {
-    "punycode": "^2.0.0"
-  },
-  "devDependencies": {
+    "punycode": "^2.0.0",
     "benchmark": "^2.1.4",
     "browserify": "^17.0.1",
     "env-test": "^1.0.0",