diff --git a/Lib/xmlrpclib.py b/Lib/xmlrpclib.py
index 3a2c0bf..e072f71 100644
--- a/Lib/xmlrpclib.py
+++ b/Lib/xmlrpclib.py
@@ -784,6 +784,7 @@
         self._stack = []
         self._marks = []
         self._data = []
+        self._value = False
         self._methodname = None
         self._encoding = "utf-8"
         self.append = self._stack.append
@@ -814,6 +815,8 @@
         if tag == "array" or tag == "struct":
             self._marks.append(len(self._stack))
         self._data = []
+        if self._value and tag not in self.dispatch:
+            raise ResponseError("unknown tag %r" % tag)
         self._value = (tag == "value")
 
     def data(self, text):