diff --git a/lib/pages/server_browser.rb b/lib/pages/server_browser.rb
index 840aaa6..da32f2f 100644
--- a/lib/pages/server_browser.rb
+++ b/lib/pages/server_browser.rb
@@ -448,7 +448,11 @@ class W3DHub
           prefill: Store.settings[:server_list_username],
           accept_callback: accept_callback,
           cancel_callback: cancel_callback,
-          valid_callback: proc { |entry| entry.length.positive? }
+          # See: https://gitlab.com/danpaul88/brenbot/-/blob/master/Source/renlog.pm#L136-175
+          valid_callback: proc do |entry|
+            entry.length > 1 && entry.length < 30 && (entry =~ /(:|!|&|%| )/i).nil? &&
+              (entry =~ /[\001\002\037]/).nil? && (entry =~ /\\/).nil?
+          end
         )
       end
 
diff --git a/lib/states/prompt_dialog.rb b/lib/states/prompt_dialog.rb
index a985bd6..d02ec1e 100644
--- a/lib/states/prompt_dialog.rb
+++ b/lib/states/prompt_dialog.rb
@@ -30,7 +30,7 @@ class W3DHub
 
             stack(width: 0.5)
 
-            button "Accept", width: 0.25 do
+            @accept_button = button "Accept", width: 0.25 do
               if @options[:valid_callback]&.call(@prompt_entry.value)
                 pop_state
                 @options[:accept_callback]&.call(@prompt_entry.value)
@@ -38,6 +38,32 @@ class W3DHub
             end
           end
         end
+
+        @prompt_entry.subscribe(:changed) do
+          if @options[:valid_callback]
+            if @options[:valid_callback].call(@prompt_entry.value)
+              c = W3DHub::THEME[:Button][:border_color]
+
+              @prompt_entry.style.border_color = c
+              @prompt_entry.style.default[:border_color] = c
+              @prompt_entry.style.hover[:border_color]   = c
+              @prompt_entry.style.active[:border_color]  = c
+
+              @accept_button.enabled = true
+            else
+              c = 0xff_ff0000
+
+              @prompt_entry.style.border_color = c
+              @prompt_entry.style.default[:border_color] = c
+              @prompt_entry.style.hover[:border_color]   = c
+              @prompt_entry.style.active[:border_color]  = c
+
+              @accept_button.enabled = false
+            end
+
+            @prompt_entry.set_border_color
+          end
+        end
       end
 
       def draw