diff --git a/app/dashboard/templates/dashboard/custom_alias.html b/app/dashboard/templates/dashboard/custom_alias.html
index 2553be6b..40fa039c 100644
--- a/app/dashboard/templates/dashboard/custom_alias.html
+++ b/app/dashboard/templates/dashboard/custom_alias.html
@@ -24,8 +24,9 @@
 
         <div class="row mt-4">
           <div class="col pr-1">
-            <input name="email-prefix" class="form-control" pattern="[0-9|A-Z|a-z|-]{1,}"
-                   title="Only letter, number or dash can be used."
+            <input name="email-prefix" class="form-control"
+                   pattern="[0-9|A-Z|a-z|-|_]{1,}"
+                   title="Only letter, number, dash (-), underscore (_) can be used in alias prefix."
                    placeholder="alias prefix"
                    autofocus required>
           </div>
diff --git a/app/oauth/templates/oauth/authorize.html b/app/oauth/templates/oauth/authorize.html
index 259ef663..267822ab 100644
--- a/app/oauth/templates/oauth/authorize.html
+++ b/app/oauth/templates/oauth/authorize.html
@@ -94,8 +94,8 @@
               <div class="mt-2">OR</div>
               <div style="display: flex; align-items: center" class="mt-2">
                 <input class="form-control"
-                       pattern="[0-9|A-Z|a-z|-]{3,}"
-                       title="Only letter, number or dash can be used and alias must have at least 3 characters."
+                       pattern="[0-9|A-Z|a-z|-|_]{1,}"
+                       title="Only letter, number, dash (-), underscore (_) can be used in alias prefix."
                        style="flex-grow: 2" name="custom-email-prefix">
                 <input type="hidden" name="email-suffix" value="{{ email_suffix }}">
                 <div class="ml-2">
@@ -103,7 +103,7 @@
                 </div>
               </div>
               <small class="text-muted">
-                Alias can use letter, number, dash and must be at least 3 characters
+                Alias can use letter, number, dash and cannot be empty
               </small>
             {% endif %}
           </div>