diff --git a/Lib/test/test_xmlrpc.py b/Lib/test/test_xmlrpc.py
index 831a5a5aaed..02d9f5c650c 100644
--- a/Lib/test/test_xmlrpc.py
+++ b/Lib/test/test_xmlrpc.py
@@ -224,6 +224,20 @@ class XMLRPCTestCase(unittest.TestCase):
             self.assertIs(type(newvalue), xmlrpclib.Binary)
             self.assertIsNone(m)
 
+    def test_loads_unsupported(self):
+        ResponseError = xmlrpclib.ResponseError
+        data = '<params><param><value><spam/></value></param></params>'
+        self.assertRaises(ResponseError, xmlrpclib.loads, data)
+        data = ('<params><param><value><array>'
+                '<value><spam/></value>'
+                '</array></value></param></params>')
+        self.assertRaises(ResponseError, xmlrpclib.loads, data)
+        data = ('<params><param><value><struct>'
+                '<member><name>a</name><value><spam/></value></member>'
+                '<member><name>b</name><value><spam/></value></member>'
+                '</struct></value></param></params>')
+        self.assertRaises(ResponseError, xmlrpclib.loads, data)
+
     def test_get_host_info(self):
         # see bug #3613, this raised a TypeError
         transp = xmlrpc.client.Transport()
diff --git a/Lib/xmlrpc/client.py b/Lib/xmlrpc/client.py
index 551dce96526..bbf9ee63f76 100644
--- a/Lib/xmlrpc/client.py
+++ b/Lib/xmlrpc/client.py
@@ -640,6 +640,7 @@ class Unmarshaller:
         self._stack = []
         self._marks = []
         self._data = []
+        self._value = False
         self._methodname = None
         self._encoding = "utf-8"
         self.append = self._stack.append
@@ -669,6 +670,8 @@ class Unmarshaller:
         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):
diff --git a/Misc/NEWS b/Misc/NEWS
index 678fac1469e..86b9789b3a1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -107,6 +107,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #26873: xmlrpc now raises ResponseError on unsupported type tags
+  instead of silently return incorrect result.
+
 - Issue #26711: Fixed the comparison of plistlib.Data with other types.
 
 - Issue #24114: Fix an uninitialized variable in `ctypes.util`.