diff --git a/tests/custom_lookups/tests.py b/tests/custom_lookups/tests.py
index 5c9ee5c5ef..14f95a241b 100644
--- a/tests/custom_lookups/tests.py
+++ b/tests/custom_lookups/tests.py
@@ -133,7 +133,7 @@ class Exactly(models.lookups.Exact):
 
 class SQLFuncMixin:
     def as_sql(self, compiler, connection):
-        return '%s()', [self.name]
+        return '%s()' % self.name, []
 
     @property
     def output_field(self):