diff --git a/configure.ac b/configure.ac
index 27a6082..1429253 100644
--- a/configure.ac
+++ b/configure.ac
@@ -82,6 +82,10 @@
 AC_DEFINE_UNQUOTED([PIM_PERSIST_PATH], ["$PIM_PERSIST_PATH"], \
     [Path of directory housing persisted inventory])
 
+AC_ARG_VAR(CLASS_VERSION, [Class version to register with Cereal])
+AS_IF([test "x$CLASS_VERSION" == "x"], [CLASS_VERSION=1])
+AC_DEFINE_UNQUOTED([CLASS_VERSION], [$CLASS_VERSION], [Class version to register with Cereal])
+
 # Create configured output
 AC_CONFIG_FILES([Makefile.extra],
     [${srcdir}/generate_makefile.sh $yaml > Makefile.extra],