diff --git a/lib/gitlab/o_auth/auth_hash.rb b/lib/gitlab/o_auth/auth_hash.rb
index d94b104bbf8..ba31599432b 100644
--- a/lib/gitlab/o_auth/auth_hash.rb
+++ b/lib/gitlab/o_auth/auth_hash.rb
@@ -62,7 +62,7 @@ module Gitlab
       # Get the first part of the email address (before @)
       # In addtion in removes illegal characters
       def generate_username(email)
-        email.match(/^[^@]*/)[0].parameterize
+        email.match(/^[^@]*/)[0].mb_chars.normalize(:kd).gsub(/[^\x00-\x7F]/,'').to_s
       end
 
       def generate_temporarily_email(username)
diff --git a/spec/lib/gitlab/o_auth/auth_hash_spec.rb b/spec/lib/gitlab/o_auth/auth_hash_spec.rb
index a4f8b44e38e..8aaeb5779d3 100644
--- a/spec/lib/gitlab/o_auth/auth_hash_spec.rb
+++ b/spec/lib/gitlab/o_auth/auth_hash_spec.rb
@@ -14,7 +14,7 @@ describe Gitlab::OAuth::AuthHash, lib: true do
   let(:uid_raw) do
     "CN=Onur K\xC3\xBC\xC3\xA7\xC3\xBCk,OU=Test,DC=example,DC=net"
   end
-  let(:email_raw) { "onur.k\xC3\xBC\xC3\xA7\xC3\xBCk@example.net" }
+  let(:email_raw) { "onur.k\xC3\xBC\xC3\xA7\xC3\xBCk_ABC-123@example.net" }
   let(:nickname_raw) { "ok\xC3\xBC\xC3\xA7\xC3\xBCk" }
   let(:first_name_raw) { 'Onur' }
   let(:last_name_raw) { "K\xC3\xBC\xC3\xA7\xC3\xBCk" }
@@ -66,7 +66,7 @@ describe Gitlab::OAuth::AuthHash, lib: true do
     before { info_hash.delete(:nickname) }
 
     it 'takes the first part of the email as username' do
-      expect(auth_hash.username).to eql 'onur-kucuk'
+      expect(auth_hash.username).to eql 'onur.kucuk_ABC-123'
     end
   end