1 files changed, 13 insertions, 3 deletions
diff --git a/Lib/xmlrpclib.py b/Lib/xmlrpclib.py
index 6fb6c68db5..3864dadc0b 100644
--- a/Lib/xmlrpclib.py
+++ b/Lib/xmlrpclib.py
@@ -630,9 +630,19 @@ class Marshaller:
         try:
             f = self.dispatch[type(value)]
         except KeyError:
-            raise TypeError, "cannot marshal %s objects" % type(value)
-        else:
-            f(self, value, write)
+            # check if this object can be marshalled as a structure
+            try:
+                value.__dict__
+            except:
+                raise TypeError, "cannot marshal %s objects" % type(value)
+            # check if this class is a sub-class of a basic type,
+            # because we don't know how to marshal these types
+            # (e.g. a string sub-class)
+            for type_ in type(value).__mro__:
+                if type_ in self.dispatch.keys():
+                    raise TypeError, "cannot marshal %s objects" % type(value)
+            f = self.dispatch[InstanceType]
+        f(self, value, write)
 
     def dump_nil (self, value, write):
         if not self.allow_none: