diff --git a/tests/lookup/models.py b/tests/lookup/models.py
index 86f774ea11..9bb3412c33 100644
--- a/tests/lookup/models.py
+++ b/tests/lookup/models.py
@@ -50,11 +50,22 @@ class NulledTextField(models.TextField):
         return None if value == "" else value
 
 
+class NullField(models.Field):
+    pass
+
+
+NullField.register_lookup(IsNull)
+
+
 @NulledTextField.register_lookup
 class NulledTransform(models.Transform):
     lookup_name = "nulled"
     template = "NULL"
 
+    @property
+    def output_field(self):
+        return NullField()
+
 
 @NulledTextField.register_lookup
 class IsNullWithNoneAsRHS(IsNull):