diff --git a/django/core/mail/__init__.py b/django/core/mail/__init__.py
index d7a868dfc2b..8d064223cd9 100644
--- a/django/core/mail/__init__.py
+++ b/django/core/mail/__init__.py
@@ -87,7 +87,7 @@ def mail_admins(subject, message, fail_silently=False, connection=None):
     """Sends a message to the admins, as defined by the ADMINS setting."""
     if not settings.ADMINS:
         return
-    EmailMessage(settings.EMAIL_SUBJECT_PREFIX + subject, message,
+    EmailMessage(u'%s%s' % (settings.EMAIL_SUBJECT_PREFIX, subject), message,
                  settings.SERVER_EMAIL, [a[1] for a in settings.ADMINS],
                  connection=connection).send(fail_silently=fail_silently)
 
@@ -96,7 +96,7 @@ def mail_managers(subject, message, fail_silently=False, connection=None):
     """Sends a message to the managers, as defined by the MANAGERS setting."""
     if not settings.MANAGERS:
         return
-    EmailMessage(settings.EMAIL_SUBJECT_PREFIX + subject, message,
+    EmailMessage(u'%s%s' % (settings.EMAIL_SUBJECT_PREFIX, subject), message,
                  settings.SERVER_EMAIL, [a[1] for a in settings.MANAGERS],
                  connection=connection).send(fail_silently=fail_silently)
 
diff --git a/tests/regressiontests/mail/tests.py b/tests/regressiontests/mail/tests.py
index b0c60d836e4..d2f7562d8f4 100644
--- a/tests/regressiontests/mail/tests.py
+++ b/tests/regressiontests/mail/tests.py
@@ -343,3 +343,23 @@ class MailTests(TestCase):
         settings.ADMINS = old_admins
         settings.MANAGERS = old_managers
 
+    def test_mail_prefix(self):
+        """Test prefix argument in manager/admin mail."""
+        # Regression for #13494.
+        old_admins = settings.ADMINS
+        old_managers = settings.MANAGERS
+        settings.ADMINS = settings.MANAGERS = [('nobody','nobody@example.com')]
+
+        mail_managers(ugettext_lazy('Subject'), 'Content')
+        self.assertEqual(len(mail.outbox), 1)
+        message = mail.outbox[0]
+        self.assertEqual(message.subject, '[Django] Subject')
+
+        mail.outbox = []
+        mail_admins(ugettext_lazy('Subject'), 'Content')
+        self.assertEqual(len(mail.outbox), 1)
+        message = mail.outbox[0]
+        self.assertEqual(message.subject, '[Django] Subject')
+
+        settings.ADMINS = old_admins
+        settings.MANAGERS = old_managers