diff --git a/api/Android.bp b/api/Android.bp
index 2c6cade..5b65e91 100644
--- a/api/Android.bp
+++ b/api/Android.bp
@@ -179,8 +179,10 @@
     cmd: metalava_cmd +
         "--check-compatibility:api:released $(location :android.api.module-lib.latest) " +
         // Note: having "public" be the base of module-lib is not perfect -- it should
-        // ideally be a merged public+system), but this will  help when migrating from
-        // MODULE_LIBS -> public.
+        // ideally be a merged public+system (which metalava is not currently able to generate).
+        // This "base" will help when migrating from MODULE_LIBS -> public, but not when
+        // migrating from MODULE_LIBS -> system (where it needs to instead be listed as
+        // an incompatibility).
         "--check-compatibility:base $(location :frameworks-base-api-current.txt) " +
         "--baseline:compatibility:released $(location :android-incompatibilities.api.module-lib.latest) " +
         "--update-baseline:compatibility:released $(genDir)/updated-baseline.txt " +