diff --git a/asu/api.py b/asu/api.py
index 8c85d716..4e3632dd 100644
--- a/asu/api.py
+++ b/asu/api.py
@@ -107,7 +107,7 @@ def validate_request(req):
 
     req["packages"] = list(
         map(
-            lambda x: x.remove_prefix("+"),
+            lambda x: x.removeprefix("+"),
             sorted(req.get("packages_versions", {}).keys() or req.get("packages", [])),
         )
     )