diff --git a/js/lib/input_validations.js b/js/lib/input_validations.js
index 8ed6341a..94ed9f5a 100644
--- a/js/lib/input_validations.js
+++ b/js/lib/input_validations.js
@@ -47,6 +47,12 @@ export default {
     unmask: ['(',')','-',' '],
     validationError: 'Please enter a 10-digit phone number'
   },
+  phoneExt: {
+    mask: [/\w/, /\w/, /\w/, /\w/, /\w/, /\w/, /\w/, /\w/, /\w/, /\w/],
+    match: /^\w*$/,
+    unmask: [],
+    validationError: 'Optional: Please enter up to 10 characters'
+  },
   dodId: {
     mask: createNumberMask({ prefix: '', allowDecimal: false, includeThousandsSeparator: false }),
     match: /^\d{10}$/,
diff --git a/templates/components/phone_input.html b/templates/components/phone_input.html
index e0e35f00..62a1c18a 100644
--- a/templates/components/phone_input.html
+++ b/templates/components/phone_input.html
@@ -6,7 +6,7 @@
         {{ TextInput(phone_number, placeholder=placeholder_phone, validation='usPhone') }}
       </div>
       <div class='phone-input__extension'>
-        {{ TextInput(phone_ext)}}
+        {{ TextInput(phone_ext, validation='phoneExt')}}
       </div>
   </div>
 {%- endmacro %}