diff --git a/django/test/testcases.py b/django/test/testcases.py
index 1acc39fd761..5533c01db45 100644
--- a/django/test/testcases.py
+++ b/django/test/testcases.py
@@ -566,7 +566,7 @@ class SimpleTestCase(unittest.TestCase):
     def _assert_form_error(self, form, field, errors, msg_prefix, form_repr):
         if not form.is_bound:
             self.fail(
-                f"{msg_prefix} The {form_repr} is not bound, it will never have any "
+                f"{msg_prefix}The {form_repr} is not bound, it will never have any "
                 f"errors."
             )
 
diff --git a/tests/test_utils/tests.py b/tests/test_utils/tests.py
index 506773b7128..92778439ed6 100644
--- a/tests/test_utils/tests.py
+++ b/tests/test_utils/tests.py
@@ -1448,6 +1448,9 @@ class AssertFormErrorTests(SimpleTestCase):
         response = mock.Mock(context=[{"form": TestForm()}])
         with self.assertRaisesMessage(AssertionError, msg):
             self.assertFormError(response, "form", "field", [])
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormError(response, "form", "field", [], msg_prefix=msg_prefix)
 
     def test_empty_errors_valid_form(self):
         response = mock.Mock(context=[{"form": TestForm.valid()}])