diff --git a/Lib/test/test_warnings/__init__.py b/Lib/test/test_warnings/__init__.py
index a04759ee0678d0..58afa59e76218a 100644
--- a/Lib/test/test_warnings/__init__.py
+++ b/Lib/test/test_warnings/__init__.py
@@ -1634,6 +1634,21 @@ def d():
             py_warnings.simplefilter("error")
             d()
 
+    def test_only_strings_allowed(self):
+        with self.assertRaisesRegex(
+            TypeError,
+            "Expected an object of type str for 'msg', not 'type'"
+        ):
+            @deprecated
+            class Foo: ...
+
+        with self.assertRaisesRegex(
+            TypeError,
+            "Expected an object of type str for 'msg', not 'function'"
+        ):
+            @deprecated
+            def foo(): ...
+
 
 def setUpModule():
     py_warnings.onceregistry.clear()
diff --git a/Lib/warnings.py b/Lib/warnings.py
index 22a1b16907959f..ce592040a3cea6 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -557,6 +557,10 @@ def __init__(
         category: type[Warning] | None = DeprecationWarning,
         stacklevel: int = 1,
     ) -> None:
+        if not isinstance(msg, str):
+            raise TypeError(
+                f"Expected an object of type str for 'msg', not {type(msg).__name__!r}"
+            )
         self.msg = msg
         self.category = category
         self.stacklevel = stacklevel