diff --git a/extensions/openpower-pels/user_data.cpp b/extensions/openpower-pels/user_data.cpp
index 45404f3..8036131 100644
--- a/extensions/openpower-pels/user_data.cpp
+++ b/extensions/openpower-pels/user_data.cpp
@@ -42,7 +42,7 @@
     stream >> _data;
 }
 
-void UserData::flatten(Stream& stream)
+void UserData::flatten(Stream& stream) const
 {
     stream << _header << _data;
 }