diff --git a/docs/user-guide.rst b/docs/user-guide.rst
index fe8ce5f..b9f0871 100644
--- a/docs/user-guide.rst
+++ b/docs/user-guide.rst
@@ -1219,11 +1219,13 @@
     make PLAT=<platform> [DEBUG=1] [V=1] certtool
 
 For platforms that require their own IDs in certificate files, the generic
-'cert_create' tool can be built with the following command:
+'cert_create' tool can be built with the following command. Note that the target
+platform must define its IDs within a ``platform_oid.h`` header file for the
+build to succeed.
 
 ::
 
-    make USE_TBBR_DEFS=0 [DEBUG=1] [V=1] certtool
+    make PLAT=<platform> USE_TBBR_DEFS=0 [DEBUG=1] [V=1] certtool
 
 ``DEBUG=1`` builds the tool in debug mode. ``V=1`` makes the build process more
 verbose. The following command should be used to obtain help about the tool: