diff --git a/evds/__init__.py b/evds/__init__.py
index 4777f98..b24f965 100644
--- a/evds/__init__.py
+++ b/evds/__init__.py
@@ -187,10 +187,10 @@ def get_data(self, series, startdate, enddate="", aggregation_types="", formulas
             formula_param = ''
         elif isinstance(formulas, list):
             # User defined formula per series
-            formula_param = "-".join([str(i) for i in formulas])
+            formula_param = "#".join([str(i) for i in formulas])
         else:
             # User defined formula same for all series
-            formula_param = "-".join([str(formulas)
+            formula_param = "#".join([str(formulas)
                                      for i in range(series_count)])
 
         data = self.__make_request('https://evds2.tcmb.gov.tr/service/evds/',