diff --git a/sqlite_utils/db.py b/sqlite_utils/db.py
index 18a442a..25c0a70 100644
--- a/sqlite_utils/db.py
+++ b/sqlite_utils/db.py
@@ -1791,7 +1791,7 @@ class Table(Queryable):
                 magic_lookup_column=magic_lookup_column,
                 lookup_table=table,
                 where=" AND ".join(
-                    "[{table}].[{column}] = [{lookup_table}].[{lookup_column}]".format(
+                    "[{table}].[{column}] IS [{lookup_table}].[{lookup_column}]".format(
                         table=self.name,
                         lookup_table=table,
                         column=column,