diff --git a/extensions/openpower-pels/user_header.cpp b/extensions/openpower-pels/user_header.cpp
index 8092e38..0014b57 100644
--- a/extensions/openpower-pels/user_header.cpp
+++ b/extensions/openpower-pels/user_header.cpp
@@ -34,7 +34,7 @@
         _actionFlags >> _reserved4Byte2;
 }
 
-void UserHeader::flatten(Stream& stream)
+void UserHeader::flatten(Stream& stream) const
 {
     stream << _header << _eventSubsystem << _eventScope << _eventSeverity
            << _eventType << _reserved4Byte1 << _problemDomain << _problemVector