diff --git a/Orange/widgets/visualize/owsieve.py b/Orange/widgets/visualize/owsieve.py
index 7c44164344e..245cde8a4a8 100644
--- a/Orange/widgets/visualize/owsieve.py
+++ b/Orange/widgets/visualize/owsieve.py
@@ -183,6 +183,8 @@ def set_data(self, data):
         self.openContext(self.data)
         if self.data:
             self.discrete_data = self.sparse_to_dense(data, True)
+            if self.discrete_data.is_sparse():
+                self.discrete_data.X = self.discrete_data.X.toarray()
         self.resolve_shown_attributes()
         self.update_graph()
         self.update_selection()
@@ -223,7 +225,8 @@ def discretizer(data):
                      self.attr_y}
             new_domain = data.domain.select_columns(attrs)
             data = Table.from_table(new_domain, data)
-            data.X = data.X.toarray()
+            if data.is_sparse():
+                data.X = data.X.toarray()
         return discretizer(data)
 
     @Inputs.features