diff --git a/pymisp/tools/domainipobject.py b/pymisp/tools/domainipobject.py
index 8da3944..62dc554 100644
--- a/pymisp/tools/domainipobject.py
+++ b/pymisp/tools/domainipobject.py
@@ -15,8 +15,8 @@ class DomainIPObject(AbstractMISPObjectGenerator):
         self.generate_attributes()
 
     def generate_attributes(self):
-        first = self._sanitize_timestamp(self.__parameters.pop('first-seen', None))
+        first = self._sanitize_timestamp(self._parameters.pop('first-seen', None))
         self._parameters['first-seen'] = first
-        last = self._sanitize_timestamp(self.__parameters.pop('last-seen', None))
+        last = self._sanitize_timestamp(self._parameters.pop('last-seen', None))
         self._parameters['last-seen'] = last
         return super(DomainIPObject, self).generate_attributes()