diff --git a/banchanHelp.sh b/banchanHelp.sh
index af7294c..eab22e4 100755
--- a/banchanHelp.sh
+++ b/banchanHelp.sh
@@ -6,7 +6,7 @@
 cd ../..
 TOP="${PWD}"
 
-message='usage: banchan <module> ... [arm|x86|arm64|x86_64] [eng|userdebug|user]
+message='usage: banchan <module> ... [<product>|arm|x86|arm64|x86_64] [eng|userdebug|user]
 
 banchan selects individual APEX modules to be built by the Android build system.
 Like "tapas", "banchan" does not request the building of images for a device but
@@ -19,6 +19,11 @@
 The module names should match apex{} modules in Android.bp files, typically
 starting with "com.android.".
 
+The product argument should be a product name ending in "_<arch>", where <arch>
+is one of arm, x86, arm64, x86_64. It can also be just an arch, in which case
+the standard product for building modules with that architecture is used, i.e.
+module_<arch>.
+
 The usage of the other arguments matches that of the rest of the platform
 build system and can be found by running `m help`'