diff --git a/Documentation/Makefile.build.txt b/Documentation/Makefile.build.txt
index 9d0f82c67..3157d7b3e 100644
--- a/Documentation/Makefile.build.txt
+++ b/Documentation/Makefile.build.txt
@@ -70,6 +70,9 @@ asm-e::
 lib-e::
 	Some extarnal library the 'built-in.o' should link with.
 
+lib-so::
+	Tells the make engine to build a shared library.
+
 incdeps::
 	A flag which tells the script to generate dependency (that named '*.d'
 	files)	for source code C files. To turn this functionality on just