diff --git a/sorteerhoed/HITStore.py b/sorteerhoed/HITStore.py
index 4ea1556..e4175ce 100644
--- a/sorteerhoed/HITStore.py
+++ b/sorteerhoed/HITStore.py
@@ -181,7 +181,10 @@ class Assignment(Base):
     def toDict(self) -> dict:
         values = {c.name: getattr(self, c.name) for c in self.__table__.columns}
         if self.turk_country:
-            values['turk_country_code'] = cc.convert([self.turk_country], to='ISO2')
+            if self.turk_country == 'Unknown':
+                values['turk_country_code'] = '--'
+            else:
+                values['turk_country_code'] = cc.convert([self.turk_country], to='ISO2')
         else:
             values['turk_country_code'] = None
         return values
@@ -192,7 +195,10 @@ class Assignment(Base):
             'turk_country': self.turk_country
         }
         if self.turk_country:
-            values['turk_country_code'] = cc.convert([self.turk_country], to='ISO2')
+            if self.turk_country == 'Unknown':
+                values['turk_country_code'] = '--'
+            else:
+                values['turk_country_code'] = cc.convert([self.turk_country], to='ISO2')
         else:
             values['turk_country_code'] = None
         return values