diff --git a/extensions/openpower-pels/mru.cpp b/extensions/openpower-pels/mru.cpp
index 78ce6b4..a79c026 100644
--- a/extensions/openpower-pels/mru.cpp
+++ b/extensions/openpower-pels/mru.cpp
@@ -53,7 +53,7 @@
     }
 }
 
-void MRU::flatten(Stream& pel)
+void MRU::flatten(Stream& pel) const
 {
     pel << _type << _size << _flags << _reserved4B;