diff --git a/scripts/perftune.py b/scripts/perftune.py
index f42b7cac1a7..b2bf18a90bd 100755
--- a/scripts/perftune.py
+++ b/scripts/perftune.py
@@ -488,7 +488,7 @@ def __learn_irqs_one(self, iface):
         if len(irqs) > 0:
             return irqs
         else:
-            return all_irqs
+            return list(all_irqs)
 
     def __learn_irqs(self):
         """