diff --git a/django/test/runner.py b/django/test/runner.py
index b22b8c3bf2..3846b3be01 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -11,6 +11,7 @@ import random
 import sys
 import textwrap
 import unittest
+from collections import defaultdict
 from contextlib import contextmanager
 from importlib import import_module
 from io import StringIO
@@ -986,21 +987,27 @@ def reorder_test_bin(tests, shuffler=None, reverse=False):
 
 def reorder_tests(tests, classes, reverse=False, shuffler=None):
     """
-    Reorder an iterable of tests by test type, removing any duplicates.
+    Reorder an iterable of tests, grouping by the given TestCase classes.
+
+    This function also removes any duplicates and reorders so that tests of the
+    same type are consecutive.
 
     The result is returned as an iterator. `classes` is a sequence of types.
-    All tests of type classes[0] are placed first, then tests of type
-    classes[1], etc. Tests with no match in classes are placed last.
+    Tests that are instances of `classes[0]` are grouped first, followed by
+    instances of `classes[1]`, etc. Tests that are not instances of any of the
+    classes are grouped last.
 
-    If `reverse` is True, sort tests within classes in opposite order but
-    don't reverse test classes.
+    If `reverse` is True, the tests within each `classes` group are reversed,
+    but without reversing the order of `classes` itself.
 
     The `shuffler` argument is an optional instance of this module's `Shuffler`
     class. If provided, tests will be shuffled within each `classes` group, but
     keeping tests with other tests of their TestCase class. Reversing is
     applied after shuffling to allow reversing the same random order.
     """
-    bins = [OrderedSet() for i in range(len(classes) + 1)]
+    # Each bin maps TestCase class to OrderedSet of tests. This permits tests
+    # to be grouped by TestCase class even if provided non-consecutively.
+    bins = [defaultdict(OrderedSet) for i in range(len(classes) + 1)]
     *class_bins, last_bin = bins
 
     for test in tests:
@@ -1009,9 +1016,11 @@ def reorder_tests(tests, classes, reverse=False, shuffler=None):
                 break
         else:
             test_bin = last_bin
-        test_bin.add(test)
+        test_bin[type(test)].add(test)
 
-    for tests in bins:
+    for test_bin in bins:
+        # Call list() since reorder_test_bin()'s input must support reversed().
+        tests = list(itertools.chain.from_iterable(test_bin.values()))
         yield from reorder_test_bin(tests, shuffler=shuffler, reverse=reverse)
 
 
diff --git a/tests/test_runner/tests.py b/tests/test_runner/tests.py
index 77a756a1de..3a535f3e1e 100644
--- a/tests/test_runner/tests.py
+++ b/tests/test_runner/tests.py
@@ -181,6 +181,19 @@ class TestSuiteTests(SimpleTestCase):
             'Tests1.test1', 'Tests1.test2', 'Tests2.test2', 'Tests2.test1',
         ])
 
+    def test_reorder_tests_same_type_consecutive(self):
+        """Tests of the same type are made consecutive."""
+        tests = self.make_tests()
+        # Move the last item to the front.
+        tests.insert(0, tests.pop())
+        self.assertTestNames(tests, expected=[
+            'Tests2.test2', 'Tests1.test1', 'Tests1.test2', 'Tests2.test1',
+        ])
+        reordered_tests = reorder_tests(tests, classes=[])
+        self.assertTestNames(reordered_tests, expected=[
+            'Tests2.test2', 'Tests2.test1', 'Tests1.test1', 'Tests1.test2',
+        ])
+
     def test_reorder_tests_random(self):
         tests = self.make_tests()
         # Choose a seed that shuffles both the classes and methods.
@@ -191,6 +204,19 @@ class TestSuiteTests(SimpleTestCase):
             'Tests2.test1', 'Tests2.test2', 'Tests1.test2', 'Tests1.test1',
         ])
 
+    def test_reorder_tests_random_mixed_classes(self):
+        tests = self.make_tests()
+        # Move the last item to the front.
+        tests.insert(0, tests.pop())
+        shuffler = Shuffler(seed=9)
+        self.assertTestNames(tests, expected=[
+            'Tests2.test2', 'Tests1.test1', 'Tests1.test2', 'Tests2.test1',
+        ])
+        reordered_tests = reorder_tests(tests, classes=[], shuffler=shuffler)
+        self.assertTestNames(reordered_tests, expected=[
+            'Tests2.test1', 'Tests2.test2', 'Tests1.test2', 'Tests1.test1',
+        ])
+
     def test_reorder_tests_reverse_with_duplicates(self):
         class Tests1(unittest.TestCase):
             def test1(self):