Index: Lib/test/test_fileio.py
===================================================================
--- Lib/test/test_fileio.py	(revision 85979)
+++ Lib/test/test_fileio.py	(working copy)
@@ -339,6 +339,7 @@
         f.truncate(15)
         self.assertEqual(f.tell(), 5)
         self.assertEqual(f.seek(0, os.SEEK_END), 15)
+        f.close()
 
     def testTruncateOnWindows(self):
         def bug801631():
Index: Modules/_io/fileio.c
===================================================================
--- Modules/_io/fileio.c	(revision 85979)
+++ Modules/_io/fileio.c	(working copy)
@@ -396,8 +396,11 @@
            end of file (otherwise, it might be done only on the
            first write()). */
         PyObject *pos = portable_lseek(self->fd, NULL, 2);
-        if (pos == NULL)
+        if (pos == NULL) {
+            close(self->fd);
+            self->fd = -1;
             goto error;
+        }
         Py_DECREF(pos);
     }