diff --git a/lib/devtools.js b/lib/devtools.js
index e28c5ae..dce1b0d 100644
--- a/lib/devtools.js
+++ b/lib/devtools.js
@@ -30,6 +30,10 @@ customElements.define('developer-tooling', class extends HTMLElement {
           #change-port-show {
             display: none;
           }
+          #change-port-input {
+            width: 80px;
+          }
+
           /* hide up/down arrow for input type=number */
           input::-webkit-outer-spin-button,
           input::-webkit-inner-spin-button {
@@ -166,7 +170,13 @@ customElements.define('developer-tooling', class extends HTMLElement {
                   </span>
                   <div>
                     <form id="change-port-form" class="hidden">
-                      <input id="change-port-input" type="number" placeholder="New port" />
+                      <input
+                        id="change-port-input"
+                        type="number"
+                        placeholder="New port"
+                        min="1024"
+                        max="65535"
+                      />
                     </form>
                     <p id="change-port-error"></p>
                   </div>