diff --git a/art/attacks/evasion/auto_attack.py b/art/attacks/evasion/auto_attack.py
index a148e43b20..76e045c9cb 100644
--- a/art/attacks/evasion/auto_attack.py
+++ b/art/attacks/evasion/auto_attack.py
@@ -330,7 +330,7 @@ def __repr__(self) -> str:
             )
             auto_attack_meta = (
                 f"AutoAttack(targeted={self.targeted}, parallel_pool_size={self.parallel_pool_size}, "
-                + "num_attacks={len(self.args)})"
+                + f"num_attacks={len(self.args)})"
             )
             return f"{auto_attack_meta}\nBestAttacks:\n{best_attack_meta}"
 
@@ -342,7 +342,7 @@ def __repr__(self) -> str:
         )
         auto_attack_meta = (
             f"AutoAttack(targeted={self.targeted}, parallel_pool_size={self.parallel_pool_size}, "
-            + "num_attacks={len(self.attacks)})"
+            + f"num_attacks={len(self.attacks)})"
         )
         return f"{auto_attack_meta}\nBestAttacks:\n{best_attack_meta}"