diff --git a/lib/net/ntlm.rb b/lib/net/ntlm.rb
index eb31d8f..1768779 100644
--- a/lib/net/ntlm.rb
+++ b/lib/net/ntlm.rb
@@ -166,7 +166,18 @@ def ntlmv2_hash(user, password, target, opt={})
         else
           ntlmhash = ntlm_hash(password, opt)
         end
-        userdomain = user.upcase + target
+
+        if opt[:unicode]
+          # Uppercase operation on username containing non-ASCI characters
+          # after behing unicode encoded with `EncodeUtil.encode_utf16le`
+          # doesn't play well. Upcase should be done before encoding.
+          user_upcase = EncodeUtil.decode_utf16le(user).upcase
+          user_upcase = EncodeUtil.encode_utf16le(user_upcase)
+        else
+          user_upcase = user.upcase
+        end
+        userdomain = user_upcase + target
+
         unless opt[:unicode]
           userdomain = EncodeUtil.encode_utf16le(userdomain)
         end
diff --git a/lib/net/ntlm/encode_util.rb b/lib/net/ntlm/encode_util.rb
index 5a13e78..b800226 100644
--- a/lib/net/ntlm/encode_util.rb
+++ b/lib/net/ntlm/encode_util.rb
@@ -39,7 +39,7 @@ def self.decode_utf16le(str)
       #   the function will convert the string bytes to UTF-16LE and note the encoding as UTF-8 so that byte
       #   concatination works seamlessly.
       def self.encode_utf16le(str)
-        str.dup.force_encoding('UTF-8').encode(Encoding::UTF_16LE, Encoding::UTF_8).force_encoding('UTF-8')
+        str.dup.force_encoding('UTF-8').encode(Encoding::UTF_16LE, Encoding::UTF_8).force_encoding('ASCII-8BIT')
       end
     end
   end
diff --git a/spec/lib/net/ntlm/message/type3_spec.rb b/spec/lib/net/ntlm/message/type3_spec.rb
index f42f491..d8e261b 100644
--- a/spec/lib/net/ntlm/message/type3_spec.rb
+++ b/spec/lib/net/ntlm/message/type3_spec.rb
@@ -222,7 +222,28 @@
 
   end
 
-  describe '.serialize' do
+  describe '#serialize' do
+    context 'when the username contains non-ASCI characters' do
+      let(:t3) {
+        t2 = Net::NTLM::Message::Type2.new
+        t2.response(
+          {
+            :user => 'Hélène',
+            :password => '123456',
+            :domain => ''
+          },
+          {
+            :ntlmv2 => true,
+            :workstation => 'testlab.local'
+          }
+        )
+      }
+
+      it 'serializes without error' do
+        expect { t3.serialize }.not_to raise_error
+      end
+    end
+
     subject(:message) { described_class.create(opts) }
     context 'with the UNICODE flag set' do
       let(:opts) { {lm_response: "\x00".b, ntlm_response: '', domain: '', workstation: '', user: '', flag: Net::NTLM::DEFAULT_FLAGS[:TYPE3] | Net::NTLM::FLAGS[:UNICODE] } }
diff --git a/spec/lib/net/ntlm_spec.rb b/spec/lib/net/ntlm_spec.rb
index 00a3d9a..7114d3f 100644
--- a/spec/lib/net/ntlm_spec.rb
+++ b/spec/lib/net/ntlm_spec.rb
@@ -59,6 +59,14 @@
     end
   end
 
+  context 'when the username contains non-ASCI characters' do
+    let(:user) { 'юзер' }
+
+    it 'should return the correct ntlmv2 hash' do
+      expect(Net::NTLM::ntlmv2_hash(user, passwd, domain, { unicode: true })).to eq(["a0f4b914a37faeaee884b6b04a20faf0"].pack("H*"))
+    end
+  end
+
   it 'should generate an lm_response' do
     expect(Net::NTLM::lm_response(
         {