diff --git a/etc/defaults/make.conf b/etc/defaults/make.conf
index 7554631bfe81..3860a147548e 100644
--- a/etc/defaults/make.conf
+++ b/etc/defaults/make.conf
@@ -145,6 +145,7 @@ BDECFLAGS=	-W -Wall -ansi -pedantic -Wbad-function-cast -Wcast-align \
 #COMPAT21=	yes
 #COMPAT22=	yes
 #COMPAT3X=	yes
+#COMPAT4X=	yes
 #
 #
 # If you do not want additional documentation (some of which are
diff --git a/share/examples/etc/make.conf b/share/examples/etc/make.conf
index 7554631bfe81..3860a147548e 100644
--- a/share/examples/etc/make.conf
+++ b/share/examples/etc/make.conf
@@ -145,6 +145,7 @@ BDECFLAGS=	-W -Wall -ansi -pedantic -Wbad-function-cast -Wcast-align \
 #COMPAT21=	yes
 #COMPAT22=	yes
 #COMPAT3X=	yes
+#COMPAT4X=	yes
 #
 #
 # If you do not want additional documentation (some of which are