diff -r 6fb033af9310 Lib/test/test_pyexpat.py
--- a/Lib/test/test_pyexpat.py	Fri Apr 08 11:40:38 2011 +0100
+++ b/Lib/test/test_pyexpat.py	Fri Apr 08 10:36:16 2011 -0700
@@ -6,6 +6,7 @@
 
 from xml.parsers import expat
 
+from test import test_support
 from test.test_support import sortdict, run_unittest
 
 
@@ -217,6 +218,16 @@
         self.assertEqual(op[15], "External entity ref: (None, u'entity.file', None)")
         self.assertEqual(op[16], "End element: u'root'")
 
+        # Issue 4877: expat.ParseFile causes segfault on a closed file.
+        fp = open(test_support.TESTFN, 'wb')
+        try:
+            fp.close()
+            parser = expat.ParserCreate()
+            with self.assertRaises(ValueError):
+                parser.ParseFile(fp)
+        finally:
+            test_support.unlink(test_support.TESTFN)
+
 
 class NamespaceSeparatorTest(unittest.TestCase):
     def test_legal(self):
diff -r 6fb033af9310 Modules/pyexpat.c
--- a/Modules/pyexpat.c	Fri Apr 08 11:40:38 2011 +0100
+++ b/Modules/pyexpat.c	Fri Apr 08 10:36:16 2011 -0700
@@ -967,6 +967,12 @@
 
     if (PyFile_Check(f)) {
         fp = PyFile_AsFile(f);
+        if (!fp) {
+            PyErr_Clear();
+            PyErr_SetString(PyExc_ValueError,
+                            "attempting to parse a closed file");
+            return NULL;
+        }
     }
     else {
         fp = NULL;