diff --git a/extensions/openpower-pels/failing_mtms.hpp b/extensions/openpower-pels/failing_mtms.hpp
index bbf0b2a..65186eb 100644
--- a/extensions/openpower-pels/failing_mtms.hpp
+++ b/extensions/openpower-pels/failing_mtms.hpp
@@ -49,7 +49,7 @@
      *
      * @param[in] stream - The stream to write to
      */
-    void flatten(Stream& stream) override;
+    void flatten(Stream& stream) const override;
 
     /**
      * @brief Returns the size of this section when flattened into a PEL