diff --git a/extensions/openpower-pels/generic.cpp b/extensions/openpower-pels/generic.cpp
index baa5a04..528b46d 100644
--- a/extensions/openpower-pels/generic.cpp
+++ b/extensions/openpower-pels/generic.cpp
@@ -40,7 +40,7 @@
     stream >> _data;
 }
 
-void Generic::flatten(Stream& stream)
+void Generic::flatten(Stream& stream) const
 {
     stream << _header << _data;
 }