diff --git a/Lib/test/test_warnings/__init__.py b/Lib/test/test_warnings/__init__.py
index 4b1b4e193cb165b..ef7e332a323c5fe 100644
--- a/Lib/test/test_warnings/__init__.py
+++ b/Lib/test/test_warnings/__init__.py
@@ -545,6 +545,29 @@ class NonWarningSubclass:
                 self.module.warn('good warning category', MyWarningClass)
             self.assertIsInstance(cm.warning, Warning)
 
+    def test_simplefilter_invalid_category(self):
+        class MyWarningClass(Warning):
+            pass
+
+        class NonWarningSubclass:
+            pass
+
+        msg_regex = 'category must be a Warning subclass, not (.*)'
+
+        with self.assertRaisesRegex(TypeError, msg_regex):
+            self.module.simplefilter('always', '')
+
+        with self.assertRaisesRegex(TypeError, msg_regex):
+            self.module.simplefilter('always', NonWarningSubclass)
+
+        with self.assertRaisesRegex(TypeError, msg_regex):
+            self.module.simplefilter('always', MyWarningClass())
+
+        with original_warnings.catch_warnings(module=self.module, record=True) as w:
+            self.module.simplefilter('always', MyWarningClass)
+            self.assertEqual(len(w), 0)
+
+
 class CWarnTests(WarnTests, unittest.TestCase):
     module = c_warnings
 
diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
index 0d550204a7687fa..19664087566dc2e 100644
--- a/Lib/unittest/case.py
+++ b/Lib/unittest/case.py
@@ -274,7 +274,11 @@ def __enter__(self):
                 v.__warningregistry__ = {}
         self.warnings_manager = warnings.catch_warnings(record=True)
         self.warnings = self.warnings_manager.__enter__()
-        warnings.simplefilter("always", self.expected)
+        if isinstance(self.expected, tuple):
+            for expected in self.expected:
+                warnings.simplefilter("always", expected)
+        else:
+            warnings.simplefilter("always", self.expected)
         return self
 
     def __exit__(self, exc_type, exc_value, tb):
diff --git a/Lib/warnings.py b/Lib/warnings.py
index 691ccddfa450ad2..ad46d5e349439d8 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -176,6 +176,9 @@ def simplefilter(action, category=Warning, lineno=0, append=False):
                       "once"), "invalid action: %r" % (action,)
     assert isinstance(lineno, int) and lineno >= 0, \
            "lineno must be an int >= 0"
+    if not (isinstance(category, type) and issubclass(category, Warning)):
+        raise TypeError('category must be a Warning subclass, '
+                        'not {!r}'.format(category))
     _add_filter(action, None, category, None, lineno, append=append)
 
 def _add_filter(*item, append):
diff --git a/Misc/NEWS.d/next/Library/2022-03-18-20-48-24.bpo-16845.gWkP5A.rst b/Misc/NEWS.d/next/Library/2022-03-18-20-48-24.bpo-16845.gWkP5A.rst
new file mode 100644
index 000000000000000..9d8b12044d576ae
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-03-18-20-48-24.bpo-16845.gWkP5A.rst
@@ -0,0 +1 @@
+Validate the category of warnings.simplefilter sooner