diff --git a/django/core/management/commands/loaddata.py b/django/core/management/commands/loaddata.py
index 595e19e5e6..40d75b58e4 100644
--- a/django/core/management/commands/loaddata.py
+++ b/django/core/management/commands/loaddata.py
@@ -327,7 +327,7 @@ class Command(BaseCommand):
             else:
                 raise CommandError(
                     "Problem installing fixture '%s': %s is not a known "
-                    "serialization format." % (''.join(parts[:-1]), parts[-1]))
+                    "serialization format." % ('.'.join(parts[:-1]), parts[-1]))
         else:
             ser_fmt = None
 
diff --git a/tests/fixtures_regress/fixtures/bad_fixture1.unkn b/tests/fixtures_regress/fixtures/bad_fix.ture1.unkn
similarity index 100%
rename from tests/fixtures_regress/fixtures/bad_fixture1.unkn
rename to tests/fixtures_regress/fixtures/bad_fix.ture1.unkn
diff --git a/tests/fixtures_regress/tests.py b/tests/fixtures_regress/tests.py
index 83b007bf59..1cac151367 100644
--- a/tests/fixtures_regress/tests.py
+++ b/tests/fixtures_regress/tests.py
@@ -182,11 +182,11 @@ class TestFixtures(TestCase):
         Test for ticket #4371 -- Loading data of an unknown format should fail
         Validate that error conditions are caught correctly
         """
-        msg = "Problem installing fixture 'bad_fixture1': unkn is not a known serialization format."
+        msg = "Problem installing fixture 'bad_fix.ture1': unkn is not a known serialization format."
         with self.assertRaisesMessage(management.CommandError, msg):
             management.call_command(
                 'loaddata',
-                'bad_fixture1.unkn',
+                'bad_fix.ture1.unkn',
                 verbosity=0,
             )
 
@@ -198,7 +198,7 @@ class TestFixtures(TestCase):
         with self.assertRaisesMessage(ImportError, "No module named 'unexistent'"):
             management.call_command(
                 'loaddata',
-                'bad_fixture1.unkn',
+                'bad_fix.ture1.unkn',
                 verbosity=0,
             )