diff --git a/jsonstat/dataset.py b/jsonstat/dataset.py
index 9760c30..beebaa9 100644
--- a/jsonstat/dataset.py
+++ b/jsonstat/dataset.py
@@ -262,7 +262,7 @@ def data(self, *args, **kargs):
             raise JsonStatException('dataset not initialized')
 
         # decoding args
-        idx = self._2idx(*args, **kargs)
+        idx = str(self._2idx(*args, **kargs))
         value = self.__value[idx]
 
         #