diff --git a/src/saml2/saml.py b/src/saml2/saml.py
index 483611f1c..b2f65b506 100644
--- a/src/saml2/saml.py
+++ b/src/saml2/saml.py
@@ -169,6 +169,9 @@ def set_type(self, typ):
         except AttributeError:
             self._extatt[XSI_TYPE] = typ
 
+        if typ.startswith("xs:"):
+            self.extension_attributes["xmlns:xs"] = XS_NAMESPACE
+
     def get_type(self):
         try:
             return self.extension_attributes[XSI_TYPE]