diff --git a/Lib/test/test_pyexpat.py b/Lib/test/test_pyexpat.py
index c233bc11e31..7548924e0f8 100644
--- a/Lib/test/test_pyexpat.py
+++ b/Lib/test/test_pyexpat.py
@@ -16,22 +16,47 @@ from test.support import sortdict, run_unittest
 class SetAttributeTest(unittest.TestCase):
     def setUp(self):
         self.parser = expat.ParserCreate(namespace_separator='!')
-        self.set_get_pairs = [
-            [0, 0],
-            [1, 1],
-            [2, 1],
-            [0, 0],
-            ]
+
+    def test_buffer_text(self):
+        self.assertIs(self.parser.buffer_text, False)
+        for x in 0, 1, 2, 0:
+            self.parser.buffer_text = x
+            self.assertIs(self.parser.buffer_text, bool(x))
+
+    def test_namespace_prefixes(self):
+        self.assertIs(self.parser.namespace_prefixes, False)
+        for x in 0, 1, 2, 0:
+            self.parser.namespace_prefixes = x
+            self.assertIs(self.parser.namespace_prefixes, bool(x))
 
     def test_ordered_attributes(self):
-        for x, y in self.set_get_pairs:
+        self.assertIs(self.parser.ordered_attributes, False)
+        for x in 0, 1, 2, 0:
             self.parser.ordered_attributes = x
-            self.assertEqual(self.parser.ordered_attributes, y)
+            self.assertIs(self.parser.ordered_attributes, bool(x))
 
     def test_specified_attributes(self):
-        for x, y in self.set_get_pairs:
+        self.assertIs(self.parser.specified_attributes, False)
+        for x in 0, 1, 2, 0:
             self.parser.specified_attributes = x
-            self.assertEqual(self.parser.specified_attributes, y)
+            self.assertIs(self.parser.specified_attributes, bool(x))
+
+    def test_specified_attributes(self):
+        self.assertIs(self.parser.specified_attributes, False)
+        for x in 0, 1, 2, 0:
+            self.parser.specified_attributes = x
+            self.assertIs(self.parser.specified_attributes, bool(x))
+
+    def test_invalid_attributes(self):
+        with self.assertRaises(AttributeError):
+            self.parser.returns_unicode = 1
+        with self.assertRaises(AttributeError):
+            self.parser.returns_unicode
+
+        # Issue #25019
+        self.assertRaises(TypeError, setattr, self.parser, range(0xF), 0)
+        self.assertRaises(TypeError, self.parser.__setattr__, range(0xF), 0)
+        self.assertRaises(TypeError, getattr, self.parser, range(0xF))
 
 
 data = b'''\
@@ -514,11 +539,12 @@ class ChardataBufferTest(unittest.TestCase):
     def test_wrong_size(self):
         parser = expat.ParserCreate()
         parser.buffer_text = 1
-        def f(size):
-            parser.buffer_size = size
-
-        self.assertRaises(ValueError, f, -1)
-        self.assertRaises(ValueError, f, 0)
+        with self.assertRaises(ValueError):
+            parser.buffer_size = -1
+        with self.assertRaises(ValueError):
+            parser.buffer_size = 0
+        with self.assertRaises(TypeError):
+            parser.buffer_size = 512.0
 
     def test_unchanged_size(self):
         xml1 = b"<?xml version='1.0' encoding='iso8859'?><s>" + b'a' * 512
diff --git a/Misc/ACKS b/Misc/ACKS
index 88e55e022f4..84fd4991753 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -807,6 +807,7 @@ Joerg Lehmann
 Robert Lehmann
 Petri Lehtinen
 Luke Kenneth Casson Leighton
+John Leitch
 Tshepang Lekhonkhobe
 Marc-André Lemburg
 Mateusz Lenik
diff --git a/Misc/NEWS b/Misc/NEWS
index ac0541b1ad7..ec450ff2f3c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -81,6 +81,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #25019: Fixed a crash caused by setting non-string key of expat parser.
+  Based on patch by John Leitch.
+
 - Issue #24917: time_strftime() buffer over-read.
 
 - Issue #23144: Make sure that HTMLParser.feed() returns all the data, even
diff --git a/Modules/pyexpat.c b/Modules/pyexpat.c
index 19be0c7cc52..c4fdaafb860 100644
--- a/Modules/pyexpat.c
+++ b/Modules/pyexpat.c
@@ -1341,11 +1341,16 @@ static int
 xmlparse_setattro(xmlparseobject *self, PyObject *name, PyObject *v)
 {
     /* Set attribute 'name' to value 'v'. v==NULL means delete */
+    if (!PyUnicode_Check(name)) {
+        PyErr_Format(PyExc_TypeError,
+                     "attribute name must be string, not '%.200s'",
+                     name->ob_type->tp_name);
+        return -1;
+    }
     if (v == NULL) {
         PyErr_SetString(PyExc_RuntimeError, "Cannot delete attribute");
         return -1;
     }
-    assert(PyUnicode_Check(name));
     if (PyUnicode_CompareWithASCIIString(name, "buffer_text") == 0) {
         int b = PyObject_IsTrue(v);
         if (b < 0)