diff --git a/pytools/persistent_dict.py b/pytools/persistent_dict.py
index 17896334ad395ca8b2b526dd7b2e8fa43f8acf8e..15732c367d8f24d55fe6f551ec7de653a7dc2e86 100644
--- a/pytools/persistent_dict.py
+++ b/pytools/persistent_dict.py
@@ -174,13 +174,13 @@ class KeyBuilder(object):
     # {{{ updaters
 
     def update_for_int(self, key_hash, key):
-        key_hash.update(str(key))
+        key_hash.update(str(key).encode("utf8"))
 
     update_for_long = update_for_int
     update_for_bool = update_for_int
 
     def update_for_float(self, key_hash, key):
-        key_hash.update(repr(key))
+        key_hash.update(repr(key).encode("utf8"))
 
     if sys.version_info >= (3,):
         def update_for_str(self, key_hash, key):