Index: Modules/cPickle.c
===================================================================
--- Modules/cPickle.c	(revision 76877)
+++ Modules/cPickle.c	(working copy)
@@ -4117,7 +4117,7 @@
 	*/
 	if (self->num_marks > 0 && self->marks[self->num_marks - 1] == len) {
 		self->num_marks--;
-	} else if (len >= 0) {
+	} else if (len > 0) {
 		len--;
 		Py_DECREF(self->stack->data[len]);
 		self->stack->length = len;
Index: Lib/test/pickletester.py
===================================================================
--- Lib/test/pickletester.py	(revision 76877)
+++ Lib/test/pickletester.py	(working copy)
@@ -1100,6 +1100,15 @@
         exec teststr in {'__builtins__': builtins}, d
         d['f']()
 
+    def test_bad_input(self):
+        # Test issue4298
+        s = '\x58\0\0\0\x54'
+        self.assertRaises(EOFError, self.module.loads, s)
+        # Test issue7455
+        s = '0'
+        # XXX Why pickle do not raise UnpicklingError?
+        self.assertRaises((IndexError, cPickle.UnpicklingError),
+                          self.module.loads, s)
 
 class AbstractPersistentPicklerTests(unittest.TestCase):