diff --git a/BUILDING b/BUILDING
index 427443768739..7dfce4cb5b65 100644
--- a/BUILDING
+++ b/BUILDING
@@ -835,6 +835,11 @@ BUILDING
                    symbol table and can be used for debugging (for example
                    with a cross-gdb built by MKCROSSGDB).
 
+     mkernel=kconf
+                   Build a new kernel in modular build.  Similar to the above
+                   kernel=kconf operation, but creates intermediate per-module
+                   relocatable objects and link them to the final kernel.
+
      kernels       This command will build all kernels defined in port
                    specific release build procedure.