diff --git a/lib/sqlalchemy_ingres/base.py b/lib/sqlalchemy_ingres/base.py
index 427c212..0e3acab 100644
--- a/lib/sqlalchemy_ingres/base.py
+++ b/lib/sqlalchemy_ingres/base.py
@@ -376,8 +376,10 @@ def get_primary_keys(self, connection, table_name, schema=None, **kw):
         
         try:
             rs = connection.exec_driver_sql(sqltext, params)
-            
-            return [row[0].rstrip() for row in rs.fetchall()]
+
+            cols = [row[0].rstrip() for row in rs.fetchall()]
+            return {"constrained_columns": [] if cols is None else cols, "name": None}
+
         finally:
             if rs:
                 rs.close()