diff --git a/epdb/logic.py b/epdb/logic.py
index 586e9f24..152cf705 100644
--- a/epdb/logic.py
+++ b/epdb/logic.py
@@ -831,7 +831,7 @@ class PackageManager(object):
             elif rule.get("reactionSmarts") is not None:
                 r.smirks = rule["reactionSmarts"]
             else:
-                raise ValueError("No SMIRKS or reactionSmarts found for rule {}".format(rule["id"]))
+                raise ValueError(f"No SMIRKS or reactionSmarts found for rule {rule['id']}")
 
             r.reactant_filter_smarts = rule.get("reactantFilterSmarts", None)
             r.product_filter_smarts = rule.get("productFilterSmarts", None)