diff --git a/src/lib/isURL.js b/src/lib/isURL.js
index 8ae971ed6..d03603e56 100644
--- a/src/lib/isURL.js
+++ b/src/lib/isURL.js
@@ -88,6 +88,9 @@ export default function isURL(url, options) {
   // However, we need to be careful not to confuse authentication credentials (user:password@host)
   // with protocols. A colon before an @ symbol might be part of auth, not a protocol separator.
   const protocol_match = url.match(/^([a-z][a-z0-9+\-.]*):/i);
+  // Keep protocol-less hostname:port URLs on the host parsing path.
+  const host_port_match = protocol_match
+    && /^[0-9]+(?:\/|$)/.test(url.substring(protocol_match[0].length));
   let had_explicit_protocol = false;
 
   const cleanUpProtocol = (potential_protocol) => {
@@ -103,7 +106,7 @@ export default function isURL(url, options) {
     return url.substring(protocol_match[0].length);
   };
 
-  if (protocol_match) {
+  if (protocol_match && !host_port_match) {
     const potential_protocol = protocol_match[1];
     const after_colon = url.substring(protocol_match[0].length);
 
diff --git a/test/validators.test.js b/test/validators.test.js
index 5196c6fe9..9db1f1745 100644
--- a/test/validators.test.js
+++ b/test/validators.test.js
@@ -499,6 +499,7 @@ describe('Validators', () => {
         'localhost',
         'localhost:3000',
         'service-name:8080',
+        'my-3272-service:9000',
         'https://localhost',
         'http://localhost:3000',
         'http://service-name:8080',