diff --git a/pisi/api.py b/pisi/api.py
index c26eac41..64030c2b 100644
--- a/pisi/api.py
+++ b/pisi/api.py
@@ -962,7 +962,7 @@ def clearCache(all=False):
 
         # sort dictionary by value from PEP-265
         from operator import itemgetter
-        return sorted(iter(sizes.items()), key=itemgetter(1), reverse=False)
+        return sorted(iter(list(sizes.items())), key=itemgetter(1), reverse=False)
 
     def removeOrderByLimit(cacheDir, order, limit):
         totalSize = 0