diff --git a/django/forms/widgets.py b/django/forms/widgets.py
index 56ff7bb5add9..82498aa662f2 100644
--- a/django/forms/widgets.py
+++ b/django/forms/widgets.py
@@ -262,6 +262,8 @@ def merge(*lists):
             return list(dict.fromkeys(chain.from_iterable(filter(None, lists))))
 
     def __add__(self, other):
+        if not isinstance(other, Media):
+            return NotImplemented
         combined = Media()
         combined._css_lists = self._css_lists[:]
         combined._js_lists = self._js_lists[:]
diff --git a/django/utils/html.py b/django/utils/html.py
index 71122ac79e8c..63db147ff147 100644
--- a/django/utils/html.py
+++ b/django/utils/html.py
@@ -278,7 +278,7 @@ def unquote_quote(segment):
 
 class CountsDict(dict):
     def __init__(self, *args, word, **kwargs):
-        super().__init__(*args, *kwargs)
+        super().__init__(*args, **kwargs)
         self.word = word
 
     def __missing__(self, key):
diff --git a/docs/make.bat b/docs/make.bat
index 5c0627897214..bed2f7e0d374 100644
--- a/docs/make.bat
+++ b/docs/make.bat
@@ -47,7 +47,7 @@ if "%1" == "clean" (
 )
 
 if "%1" == "html" (
-	%SPHINXBUILD% -b djangohtml %ALLSPHINXOPTS% %BUILDDIR%/html
+	%SPHINXBUILD% -b html %ALLSPHINXOPTS% %BUILDDIR%/html
 	if errorlevel 1 exit /b 1
 	echo.
 	echo.Build finished. The HTML pages are in %BUILDDIR%/html.
diff --git a/tests/forms_tests/tests/test_media.py b/tests/forms_tests/tests/test_media.py
index b24ed948a955..854e52d95c9f 100644
--- a/tests/forms_tests/tests/test_media.py
+++ b/tests/forms_tests/tests/test_media.py
@@ -859,6 +859,13 @@ def test_add_empty(self):
         self.assertEqual(merged._css_lists, [{"screen": ["a.css"]}])
         self.assertEqual(merged._js_lists, [["a"]])
 
+    def test_add_invalid_type(self):
+        class InvalidType:
+            pass
+
+        with self.assertRaises(TypeError):
+            Media() + InvalidType()
+
     def test_render_js_with_attrs(self):
         media = Media(js=[Script("/path/to/js", integrity="sha256-abc")])
         self.assertHTMLEqual(
diff --git a/tests/signals/tests.py b/tests/signals/tests.py
index e304424eb8af..ea2fe39fb8e8 100644
--- a/tests/signals/tests.py
+++ b/tests/signals/tests.py
@@ -1,4 +1,5 @@
 import contextvars
+import gc
 from inspect import markcoroutinefunction
 from unittest import mock
 
@@ -14,26 +15,34 @@
 
 
 class BaseSignalSetup:
+    def _signal_counts(self):
+        # Clear dead receivers before counting.
+        counts = []
+        for signal in (
+            signals.pre_save,
+            signals.post_save,
+            signals.pre_delete,
+            signals.post_delete,
+        ):
+            with signal.lock:
+                signal._clear_dead_receivers()
+            counts.append(len(signal.receivers))
+        return tuple(counts)
+
     def setUp(self):
-        # Save up the number of connected signals so that we can check at the
-        # end that all the signals we register get properly unregistered
-        # (#9989)
-        self.pre_signals = (
-            len(signals.pre_save.receivers),
-            len(signals.post_save.receivers),
-            len(signals.pre_delete.receivers),
-            len(signals.post_delete.receivers),
-        )
+        # The count comparison in tearDown() is a regression check for
+        # Signal.disconnect() failing to remove entries (#9989). Collect first
+        # so the baseline contains only reachable receivers; a receiver
+        # connected elsewhere in the suite and then garbage-collected could
+        # linger as a dead weakref, inflating the count (#29187). No collection
+        # in tearDown(): a weak receiver kept alive by a cycle should be
+        # counted, to catch a forgotten disconnect.
+        gc.collect()
+        self.pre_signals = self._signal_counts()
 
     def tearDown(self):
         # All our signals got disconnected properly.
-        post_signals = (
-            len(signals.pre_save.receivers),
-            len(signals.post_save.receivers),
-            len(signals.pre_delete.receivers),
-            len(signals.post_delete.receivers),
-        )
-        self.assertEqual(self.pre_signals, post_signals)
+        self.assertEqual(self.pre_signals, self._signal_counts())
 
 
 class SignalTests(BaseSignalSetup, TestCase):