diff --git a/modoboa/admin/tests/mapfiles.py b/modoboa/admin/tests/mapfiles.py
index e9cfe135b..589d22cd1 100644
--- a/modoboa/admin/tests/mapfiles.py
+++ b/modoboa/admin/tests/mapfiles.py
@@ -9,8 +9,6 @@ class MapFilesTestCase(MapFilesTestCaseMixin, TestCase):
 
     """Test case for admin."""
 
-    extension = "admin"
-
     MAP_FILES = [
         "sql-domains.cf", "sql-domain-aliases.cf", "sql-aliases.cf",
         "sql-maintain.cf"
diff --git a/modoboa/lib/test_utils.py b/modoboa/lib/test_utils.py
index 55c2ab16d..3b5f070c5 100644
--- a/modoboa/lib/test_utils.py
+++ b/modoboa/lib/test_utils.py
@@ -23,9 +23,9 @@ class MapFilesTestCaseMixin(object):
     def _test_maps_generation(self, engine):
         dburl = "{0}://user:password@localhost/testdb".format(engine)
         code, output = exec_cmd(
-            "modoboa-admin.py postfix_maps --extensions {0}"
-            " --dburl {1} {2}".format(
-                self.extension, dburl, self.workdir
+            "modoboa-admin.py postfix_maps {0}--dburl {1} {2}".format(
+                "--extensions {} ".format(self.extension)
+                if self.extension else "", dburl, self.workdir
             )
         )
         self.assertEqual(code, 0)
diff --git a/modoboa/relaydomains/tests.py b/modoboa/relaydomains/tests.py
index 5effd7daf..e40654a45 100644
--- a/modoboa/relaydomains/tests.py
+++ b/modoboa/relaydomains/tests.py
@@ -245,8 +245,6 @@ class MapFilesTestCase(MapFilesTestCaseMixin, TestCase):
 
     """Test case for relaydomains."""
 
-    extension = "relaydomains"
-
     MAP_FILES = [
         "sql-relaydomains.cf",
         "sql-relaydomains-transport.cf",