diff --git a/test/fixtures/mail_handler/ticket_with_mixed_single_and_multi_bytes_subject.eml b/test/fixtures/mail_handler/ticket_with_mixed_single_and_multi_bytes_subject.eml
new file mode 100644
index 000000000..e4075a130
--- /dev/null
+++ b/test/fixtures/mail_handler/ticket_with_mixed_single_and_multi_bytes_subject.eml
@@ -0,0 +1,12 @@
+To: redmine@somenet.foo
+From: John Smith <JSmith@somenet.foo>
+Subject: =?UTF-8?B?W+e3iuaApV1bUkVETUlORV1bV0FSTklORzAxXVByb2JsZW06IOODoQ==?=
+ =?UTF-8?B?44Oi44Oq5a656YeP44GM6YC86L+r44GX44Gm44GE44G+44GZ?=
+Message-ID: <42feb4b3-4dec-7c61-0edd-45dfc4795143@somenet.foo>
+Date: Tue, 18 Jun 2019 14:08:06 +0900
+MIME-Version: 1.0
+Content-Type: text/plain; charset=utf-8; format=flowed
+Content-Language: en-US
+Content-Transfer-Encoding: 7bit
+
+Problem started at 13:49:27 on 2019.06.18
diff --git a/test/unit/mail_handler_test.rb b/test/unit/mail_handler_test.rb
index ed064f6f7..8aab1aabc 100644
--- a/test/unit/mail_handler_test.rb
+++ b/test/unit/mail_handler_test.rb
@@ -1158,6 +1158,15 @@ class MailHandlerTest < ActiveSupport::TestCase
     assert_equal 'αβγδεζηθικλμνξοπρςστυφχψω', issue.subject
   end
 
+  def test_email_with_mixed_single_and_multi_bytes_subject
+    issue = submit_email(
+              'ticket_with_mixed_single_and_multi_bytes_subject.eml',
+              :issue => {:project => 'ecookbook'}
+            )
+    assert issue.is_a?(Issue)
+    assert_equal '[緊急][REDMINE][WARNING01]Problem: メモリ容量が逼迫しています', issue.subject
+  end
+
   def test_first_keyword_should_be_matched
     issue = submit_email('ticket_with_duplicate_keyword.eml', :allow_override => 'priority')
     assert issue.is_a?(Issue)