diff --git a/aiojenkins/builds.py b/aiojenkins/builds.py
index 6425ec2..13f79d2 100644
--- a/aiojenkins/builds.py
+++ b/aiojenkins/builds.py
@@ -231,7 +231,7 @@ def format_data(parameters: Optional[dict], kwargs: Any) -> Optional[dict]:
         response = await self.jenkins._request(
             'POST',
             path,
-            params={'delay': '{0}sec'.format(delay)},
+            params={'delay': f'{delay}sec'},
             data=data,
         )