diff --git a/models/site.rb b/models/site.rb
index 365d5444..bd718849 100644
--- a/models/site.rb
+++ b/models/site.rb
@@ -683,7 +683,7 @@ class Site < Sequel::Model
   end
 
   def self.valid_username?(username)
-    !username.empty? && username.match(/^[a-zA-Z0-9]([a-zA-Z0-9_\-]{0,}[a-zA-Z0-9])?$/i) != nil
+    !username.empty? && username.match(/^[a-z0-9]([a-z0-9_\-]{0,}[a-z0-9])?$/) != nil
   end
 
   def self.disposable_email_domains_whitelist