diff --git a/extensions/openpower-pels/callouts.cpp b/extensions/openpower-pels/callouts.cpp
index 925b383..17f5bdd 100644
--- a/extensions/openpower-pels/callouts.cpp
+++ b/extensions/openpower-pels/callouts.cpp
@@ -36,7 +36,7 @@
     }
 }
 
-void Callouts::flatten(Stream& pel)
+void Callouts::flatten(Stream& pel) const
 {
     pel << _subsectionID << _subsectionFlags << _subsectionWordLength;