diff --git a/modoboa/admin/serializers.py b/modoboa/admin/serializers.py
index 3827ec139..878df8b05 100644
--- a/modoboa/admin/serializers.py
+++ b/modoboa/admin/serializers.py
@@ -5,6 +5,7 @@ from __future__ import unicode_literals
 from django.core.exceptions import ValidationError
 from django.shortcuts import get_object_or_404
 from django.utils.translation import ugettext as _, ugettext_lazy
+from django.utils.encoding import force_text
 
 from rest_framework import serializers
 from passwords import validators
@@ -77,7 +78,7 @@ class DomainAliasSerializer(serializers.ModelSerializer):
                 object_type="domain_aliases")
         except lib_exceptions.ModoboaException as inst:
             raise serializers.ValidationError({
-                "domain": unicode(inst)})
+                "domain": force_text(inst)})
         domain_alias.save(creator=creator)
         return domain_alias
 
@@ -254,7 +255,7 @@ class WritableAccountSerializer(AccountSerializer):
                 object_type="mailboxes")
         except lib_exceptions.ModoboaException as inst:
             raise serializers.ValidationError({
-                "domain": unicode(inst)})
+                "domain": force_text(inst)})
         quota = data.pop("quota", None)
         mb = admin_models.Mailbox(
             user=account, address=address, domain=domain, **data)
@@ -347,7 +348,7 @@ class AliasSerializer(serializers.ModelSerializer):
                 sender=self.__class__, context=self.domain,
                 object_type="mailbox_aliases")
         except lib_exceptions.ModoboaException as inst:
-            raise serializers.ValidationError(unicode(inst))
+            raise serializers.ValidationError(force_text(inst))
         recipients = validated_data.pop("recipients", None)
         alias = admin_models.Alias(domain=self.domain, **validated_data)
         alias.save(creator=creator)
diff --git a/modoboa/limits/tests/test_api.py b/modoboa/limits/tests/test_api.py
index d671c0c2c..ecfbe9d8f 100644
--- a/modoboa/limits/tests/test_api.py
+++ b/modoboa/limits/tests/test_api.py
@@ -114,7 +114,7 @@ class APIAdminLimitsTestCase(lib_tests.ModoAPITestCase):
         response = self.client.post(url, data, format="json")
         self.assertEqual(response.status_code, 400)
         self.assertEqual(
-            response.content,
+            response.content.decode(),
             '"You\'re not allowed to define unlimited values"')
 
     def test_domain_aliases_limit(self):
diff --git a/modoboa/limits/tests/test_import.py b/modoboa/limits/tests/test_import.py
index 7f8e4603f..dc743b438 100644
--- a/modoboa/limits/tests/test_import.py
+++ b/modoboa/limits/tests/test_import.py
@@ -31,7 +31,7 @@ class LimitImportTestCase(ModoTestCase):
         """Check domain aliases limit."""
         self.client.force_login(self.reseller)
         self.assertFalse(limit.is_exceeded())
-        f = ContentFile(b"""domainalias; domalias1.com; {domain}; True
+        f = ContentFile("""domainalias; domalias1.com; {domain}; True
 domainalias; domalias2.com; {domain}; True
 """.format(domain=self.domain), name="domains.csv")
         self.client.post(
@@ -70,7 +70,7 @@ domainalias; domalias2.com; {domain}; True
         )
         self.assertTrue(limit.is_exceeded())
 
-        f = ContentFile(b"""account; admin3@{domain}; toto; User; One; True; DomainAdmins; admin3@{domain}; 5; {domain}
+        f = ContentFile("""account; admin3@{domain}; toto; User; One; True; DomainAdmins; admin3@{domain}; 5; {domain}
 """.format(domain=self.domain), name="domain_admins.csv")
         response = self.client.post(
             reverse("admin:identity_import"), {
@@ -111,7 +111,7 @@ account; user3@{domain}; toto; User; One; True; SimpleUsers; user3@{domain}; 5
         """Check mailbox aliases limit."""
         self.client.force_login(self.dadmin)
         self.assertFalse(limit.is_exceeded())
-        f = ContentFile(b"""alias; alias1@{domain}; True; user@{domain}
+        f = ContentFile("""alias; alias1@{domain}; True; user@{domain}
 alias; alias2@{domain}; True; user@{domain}
 """.format(domain=self.domain), name="aliases.csv")
         response = self.client.post(