diff --git a/src/pycalphad_xml/CEF.rng b/src/pycalphad_xml/CEF.rng
index 412d474..590051e 100644
--- a/src/pycalphad_xml/CEF.rng
+++ b/src/pycalphad_xml/CEF.rng
@@ -105,6 +105,17 @@
                         </oneOrMore>
                     </element>
                 </optional>
+                <optional>
+                    <element name="Symmetry">
+                        <a:documentation>Specification of sublattice symmetry.</a:documentation>
+                        <attribute name="type">
+                            <choice>
+                                <value>FCC_4SL</value>
+                                <value>BCC_4SL</value>
+                            </choice>
+                        </attribute>
+                    </element>
+                </optional>
             </interleave>
         </element>
         <zeroOrMore>
diff --git a/src/pycalphad_xml/parser.py b/src/pycalphad_xml/parser.py
index b51f6ae..ca9dae5 100644
--- a/src/pycalphad_xml/parser.py
+++ b/src/pycalphad_xml/parser.py
@@ -1,4 +1,4 @@
-from pycalphad.io.tdb import _sympify_string, _process_reference_state, to_interval
+from pycalphad.io.tdb import _sympify_string, _process_reference_state, _symmetry_added_parameter, to_interval
 from pycalphad import variables as v
 from pycalphad import __version__ as pycalphad_version
 from symengine import Piecewise, And, Symbol, S
@@ -360,6 +360,7 @@ def write_xml(dbf, fd, require_valid=True):
             if ('symmetry_BCC_4SL' in model_hints.keys()):
                 if symmetry_node is not None:
                     raise ValueError('Multiple parameter symmetry options specified')
+                symmetry_node = objectify.SubElement(model_node, "Symmetry", type="BCC_4SL")
                 del model_hints['symmetry_BCC_4SL']
             # ChemicalGroups
             if "chemical_groups" in model_hints:
@@ -376,6 +377,8 @@ def write_xml(dbf, fd, require_valid=True):
             raise ValueError('Not all model hints are supported: {}'.format(model_hints))
 
     for param in dbf._parameters.all():
+        if _symmetry_added_parameter(dbf, param):
+            continue
         phase_name = param['phase_name']
         # Create phase implicitly if not defined
         if phase_nodes.get(phase_name, None) is None: