diff --git a/games/models.py b/games/models.py
index 792e8fb..5132354 100644
--- a/games/models.py
+++ b/games/models.py
@@ -212,7 +212,7 @@ class Purchase(models.Model):
                 or existing_purchase.price_currency != self.price_currency
             ):
                 self.converted_price = None
-                self.converted_currency = None
+                self.converted_currency = ""
         super().save(*args, **kwargs)
 
 
diff --git a/games/tasks.py b/games/tasks.py
index 3c960ec..4ac21fb 100644
--- a/games/tasks.py
+++ b/games/tasks.py
@@ -22,7 +22,7 @@ def save_converted_info(purchase, converted_price, converted_currency):
 
 def convert_prices():
     purchases = Purchase.objects.filter(
-        converted_price__isnull=True, converted_currency__isnull=True
+        converted_price__isnull=True, converted_currency=""
     )
 
     for purchase in purchases: