diff --git a/pyroute2/ndb/main.py b/pyroute2/ndb/main.py
index 5109a9805..599ba6b5d 100644
--- a/pyroute2/ndb/main.py
+++ b/pyroute2/ndb/main.py
@@ -304,7 +304,7 @@ def commit(self):
                     try:
                         rb.rollback()
                     except Exception as e:
-                        self.log.warning(f'ignore rollback exception: {e}')
+                        self.log.warning('ignore rollback exception: %s' % e)
                 raise
         self.event.set()
         return self