diff --git a/pycalphad/model.py b/pycalphad/model.py
index 276a7b20a..81f45d8d5 100644
--- a/pycalphad/model.py
+++ b/pycalphad/model.py
@@ -342,7 +342,7 @@ def build_reference_model(self, dbe, preserve_ideal=True):
         if preserve_ideal:
             mod_endmember_only.models['idmix'] = 0
         self.reference_model = mod_endmember_only
-        if self.models['ord'] != S.Zero:
+        if self.models.get('ord', S.Zero) != S.Zero:
                 for k in self.reference_model.models.keys():
                     self.reference_model.models[k] = nan