diff --git a/src/mvesuvio/analysis_reduction.py b/src/mvesuvio/analysis_reduction.py
index d4b89294..c03ba6b7 100644
--- a/src/mvesuvio/analysis_reduction.py
+++ b/src/mvesuvio/analysis_reduction.py
@@ -1007,7 +1007,7 @@ def _set_results(self):
         j = 0
         while True:
             try:
-                wsIterName = self._name + str(j)
+                wsIterName = self._name + '_' + str(j)
 
                 # Extract ws that were fitted
                 ws = mtd[wsIterName]